Earlier last week the San Francisco 49ers and the NFL world were shocked when Chris Borland, the 24-year old linebacker coming off his impressive rookie season, announced he would be retiring from football because of concerns for his health. Borland didn't suffer any career-ending injuries but rather decided he wanted to make the decision before his health crossed a line that it couldn't come back from. This comes after a recent string of players, including Patrick Willis, Jason Worilds and Jake Locker have also announced to be unexpectedly hanging it up early.

While the trend of early retirement is increasingly concerning for the NFL, all major sports have seen some of their stars hang it up early. The most common reason is because of injury, as some athletes' bodies fail them earlier than expected, robbing them of some of their prime years. The amount of effort and sacrifice it takes for athletes to reach their highest level is draining and at some point, it's not worth it. It is a difficult decision to walk away from something you know you can still excel at, but some players choose to leave while still on top, instead of fading into shells of the stars they once were. There always seems to be a catch 22 as to when a player should retire. Either they retire young and people say they should have played longer, or they retire several years after they've passed their prime and people fault the athlete for hanging on too long. Either way, it's no one's decision but theirs and people should accept it. No one would like someone to tell them when they should retire from their line of work.

Here is a list of 15 players that retired at a young age, be it due to injuries or they simply decided to go out on top, or they just felt they were done with the game.

15 15. Michael Jordan

Yes he went on to return to the NBA and win three more rings with the Bulls and return again as player/owner with the Washington Wizards, but the shock of MJ's 1993 retirement announcement at the top of his game, as the most famous athlete in the world, was more so shocking that rumors exist to this day around why he decided to leave the league. MJ is the best NBA player of all time and his accolades could have been even more dominating had he not taken this time off. Jordan signed a minor league deal with the Chicago White Sox, trying to make the majors before returning to the NBA in 1995. NBA teams surely were relieved to have him take some time off, particularly the Houston Rockets and New York Knicks, so that may actually have a chance at winning a championship.

14 14. Rocky Marciano

Rocky Marciano was one of the most dominant heavyweight boxers of all time as he went undefeated throughout his career. Rocky went undefeated with 43 knockouts in 49 wins before retiring at only age 32. In 1970, a radio producer decided to see who was the best heavyweight of all time, and using a computer program and probabilities, the program determined that Marciano was the best. Marciano stated that his decision to retire largely had to do with wanting to focus more on his family, a reasoning that no can fault. Marciano however ended up spending his post-boxing career getting close with the Mafia and evading his tax payments. He died in a plane crash at the age of 45.

13 13. Troy Aikman

Troy Aikman was the leader of America's team as the Cowboys won three Super Bowls during the 1990s. Aikman teamed up with Michael Irvin and Emmitt Smith to form the 'triplets' who became one of the best offenses in the 1990s. Aikman went first overall in the NFL Draft before becoming a six-time Pro-Bowler in his 12 seasons, all played with the Cowboys. Aikman decided to hang it up after the 2000 season due to persistent back pain, a situation that sounds foreboding for the Cowboys current quarterback. Troy has gone to become a successful broadcaster, who does his best to not let his Cowboys bias come through when calling their games.

12 12. Mike Bossy

Mike Bossy was one of the best players on the New York Islander teams in the early 1980's that dominated the NHL and won four Stanley Cups. Bossy scored 573 goals and 553 assists in only 752 games for an impressive 1.5 points per game and in 1980, became the just second player to score 50 goals in 50 games. Bossy was one of the defining 50-goal scorers during the NHLs golden era, reaching that peak in nine consecutive seasons, including five seasons with 60 goals. Bossy took a year off to try to rest his ailing back but was forced to hang-up his skates in 1988 at the age of 30 due to his chronic back issues but remains one the best scorers in league history. One has to wonder if he could've been the NHL's all-time leading goalscorer had he stayed healthy.

11 11. Justine Henin

Justine Henin was one the best tennis players of her generation, winning 43 singles tournaments. In 2008 and at just age 25, Henin left the sport at her peak, as the no.1 ranked tennis player in the world. Henin wanted to see what a life outside of the game could bring her. She won seven grand slams and an Olympic gold, with Wimbledon remaining the only hole in her resume. Henin excelled using her skill and speed to compete with her contemporaries who often possessed more power. Henin did mount a return to the court but retired for good at age 28 due to an elbow injury.

10 10. Bo Jackson

Bo Jackson was as physically gifted an athlete as there has ever been as he became an all-star in both the NFL and MLB. His career seems like it's fantasy as the idea of an athlete excelling at two major sports in the same season is difficult to fathom nowadays. He finished his baseball career as .250 hitter with 141 home runs and showed off his athleticism in the outfield. As a football player, Jackson had a 5.4 yards per carry average and 2,872 yards in his time with the Raiders. Bo Jackson retired from football at age 28 and baseball at age 32. In a generation where kids are now forced to decide on one sport at earlier and earlier ages, it would be smart to take note of Bo's amazing career.

9 9. Isiah Thomas

While Isiah Thomas has tarnished his legacy a bit in his post-playing career, it's important to remember he was one of the best players of his generation and the definition of a true point guard. Thomas was the leader of the Pistons in the 1980s, leading them to consecutive titles. Thomas averaged 19 points and 9 assists per game during his career, thriving despite his diminutive stature. Thomas was one the best point guards of all time despite lacking an outside shot, shooting only 29% from the 3-point arc during his career. Thomas relied on his ability to get to the basket at will and set his teammates up for success. After suffering a traumatic achilles injury, Thomas announced his retirement at age 32. "Zeke" went on to hold a number of positions in the league including coach, general manager and part-owner.

8 8. Barry Sanders

Some retirements are so unexpected that they can set a franchise back for years, as Sanders's announcement did with the Lions. Sanders led the Lions to some of the best years in their franchise history, going to the playoffs five times in his career. During the 1997 season Sanders won co-MVP with Brett Favre after running for over 2,000 yards. Sanders is the most elusive runner in NFL history, routinely making tacklers miss the backfield. Today's most elusive runners, such as LeSean McCoy often get the Sanders comparison for his running style. The 10-time Pro-Bowler summed up his decision up nicely by saying:

"My desire to exit the game is greater than my desire to remain in it." Despite his stellar play he found it difficult to deal with the Lions' losing record in his final years and admitted that played a role in his decision to hang it up.

7 7. Yao Ming

The 7-foot-6 Yao Ming came into the NBA in 2002 with no shortage of hype as the first overall pick. While his career may have started off slow as he learned the NBA game and became more comfortable in the U.S., Ming eventually solidified himself as one of the biggest stars in the game. Ming often led the league in votes for the all-star game as he was a massive star in his homeland China. At his peak, Yao combined his size and skill to average 26.6 PPG, 10 RPG and 2 BPG per 36 minutes, with a Player Efficiency Rating of 26.5. Yao unfortunately injured his foot in the playoffs in 2009 and played just five more games in his NBA career before retiring at age 30. Yao was an 8-time NBA All-Star during his career but it's tough to look back and not think of what could have been between the pairing of him and Tracey McGrady.

6 6. Brandon Roy

Brandon Roy was developing into one of the best young players in the league when he started his career by winning Rookie of the Year in 2006-07. Roy made three consecutive All-Star games and was all-NBA two years in a row. Brandon was an all-around player who could score in a multitude of ways and seemed to be the next best two-guard in the association. Roy was drafted with knee concerns so it was not all that unexpected when they began to flare up into his career. Roy suffered through multiple knee surgeries and attempted to attempt his game to his diminished athleticism and increased pain. Roy announced his retirement for good from the NBA after a brief comeback attempt with the Timberwolves in 2013 at age 29, during what should have been the prime years of his career.

5 5. Gale Sayers

Gale Sayers exploded into his NFL career setting a rookie record with 22 touchdowns as a running back and a devastating kick returner. Sayers revolutionized the running back position becoming one of the first to be a significant receiving threat. Sayers made the Pro Bowl five times in his short career and averaged over five yards per carry. Sayers was a walking highlight film and its a testament to his ability that he was elected as a first-ballot hall of famer despite playing less than 70 games. After battling back from a number of serious knee injuries, Sayers called it quits in 1971 at only 28 years old.

4 4. Bjorn Borg

Bjorn Borg was one of the first superstars in Tennis, winning 11 Grand Slam titles including five consecutive Wimbledon titles. Bjorn was a teenage phenom winning his first prominent singles tournament at age 18 and went on to set the record as the youngest Wimbledon winner ever at that time at age 20, without dropping a set. Borg was known for his powerful backhand, steller play from the back line of the court and his unrivaled stamina on the court. Borg retired at only age 26 but played at very high levels since he was 15. Borg decided his heart was no longer in the game and that he couldn't compete the way he wanted to. Borg went on to start a successful fashion line and remain involved in the tennis world.

3 3. Bobby Orr

Bobby Orr is considered the best defenseman in the history of the NHL and many argue he's the sport's best player ever, as he led the Bruins to two Stanley Cup trophies. Orr was known as a revolutionary player who showed that defensemen could play a more prominent role offensively. Orr was known for his end-to-end rushes showing the speed and skills of a forward. Orr won eight consecutive Norris Trophies as the best defenseman in the league and finished his career with 270 goals and 645 assists. After signing with the Chicago Blackhawks in 1976, Orr struggled through injuries before deciding to retire in 1978. It was an unfortunate end that didn't fit his amazing career that should have ended with the Boston Bruins.

2 2. Jim Brown

Jim Brown epitomized the NFL during his nine seasons, leading the league in rushing in eight of those seasons and winning league MVP three times. He is still to this day the only running back to average over 100 yards a game for his career. Jim Brown was a huge running back who played at 228 pounds and was impossible to tackle but had the speed and grace of a smaller runner. Brown was showing no signs of decline when he decided to retire at age 29 as he ran for 1,544 yards and 21 touchdowns in his last season. Jim Brown is considered by many as the best football player of all time, an honor that the Sporting News bestowed on him in 2002. Jim Brown went on to have a successful acting career in films such as the Dirty Dozen and is by the far the most important Cleveland Brown of all time.

1 1. Magic Johnson

Few athletes were as charismatic and fun as Magic Johnson was playing with the showtime Lakers. Magic took the league by storm winning the NBA championship, his first of five, in his first season, while picking up NBA finals MVP. After winning three MVPs and making 12 All Star games, Magic was forced to retire in 1991 at the age 32 after tests revealed he was HIV positive. Magic went on to attempt several comebacks but his largest achievements were what he did for reducing the stigma associated with HIV. Magic was voted to the All Star game in 1991 despite missing the season and the statement he made by playing and the support the other players showed him went a long way. Magic has gone on to become a successful businessman and sports commentator. Magic is easily one of the 10 best players of all time and his rivalry with Larry Bird helped grow the league to where it is today.