Well, that's not good. According to a post from ESPN (who we believe broke this first), UFC has been informed of a possible infraction by The Beast Incarnate:
The UFC has been notified of a potential anti-doping violation by Brock Lesnar, stemming from June 28.— Brett Okamoto (@bokamotoESPN) July 15, 2016
Yesterday, news broke that Brock Lesnar was still under contract with the UFC and that he'd still be tested by the USADA. Well, it turns out that one of those tests may have shown something. If that would be the case, a no contest would be likely for Lesnar's fight with Mark Hunt. Could this also lead to a suspension from the WWE?
We'll update the post as more information becomes available.