The United States Anti-Doping Agency has informed Brock Lesnar of a potential doping violation stemming from an out-of-competition drug test administered June 28.
Lesnar, 39, returned to the Octagon on July 9, defeating Mark Hunt via decision at UFC 200. It was Lesnar's first fight since December 2011. The pro wrestling star remains under contract with WWE and has declined to say whether he would fight in a UFC match again.
The UFC announced Lesnar's potential violation on Friday. In a statement, the UFC said it was not informed of the potential violation until Thursday, which explains why Lesnar was able to compete on the UFC 200 card.
Lesnar told The Associated Press in a statement, "We will get to the bottom of this."
In an interview with MMA Fighting on Friday, Hunt said he has asked UFC officials for half of Lesnar's record $2.5 million guaranteed purse or to be released from his contract effective immediately. Hunt added he has yet to hear from the UFC.
"The cheaters get a slap on the wrist and walk off," Hunt told MMA Fighting. "What penalty or deterrent is there to make them think twice? Nothing. And the [Nevada Athletic Commission], why should these [expletive] get anything? They are not the ones who had to fight with Lesnar or lose [to him]. I lost."
Hunt changed his tone later Friday night in a profanity-laced tweet, saying that he now wants all of Lesnar's guaranteed purse.
"Well I wanted half but have changed my mind cheaters shouldn't get s--- I want all of it cheaters don't deserve s---," Hunt wrote in his tweet.
Under the UFC's anti-doping program, which is administered by USADA and went into effect in July 2015, results management and adjudication of the case falls to USADA, as well as the Nevada State Athletic Commission, due to the fact Lesnar's fight took place in Las Vegas.
Bob Bennett, executive officer of the NSAC, told the Los Angeles Times that Lesnar's purse could be factored in assessing the size of a potential fine.
"Exactly, right," Bennett told the newspaper.
"We can fine and suspend. I'm not saying his whole paycheck will be taken away, but he could be suspended and fined upon his case being heard and all the facts being presented."
The NSAC already is involved in another case regarding UFC 200. Former light heavyweight champion Jon Jones, who was removed from UFC 200 three days prior to the event because of a potential violation, is also facing discipline from the NSAC.
Lesnar (6-3) announced his retirement from mixed martial arts in 2015, but ultimately decided to return to the UFC for a "one-off," to which WWE agreed.
Lesnar has not before tested positive for banned substances in his UFC career. It also is unknown at this time whether the potential doping violation is for a banned substance or a banned methodology.
Under the UFC's program, any retired athlete who wishes to return to competition must first be subjected to a four-month testing window.
The UFC is able to grant exemptions to that requirement, however. Because of the unique circumstances of Lesnar's return and his contract situation with WWE, the UFC decided to waive that four-month window for the first time.
Despite receiving an exemption for the four-month requirement, Lesnar did submit eight tests to USADA, according to the agency's website.
Hunt, 42, referenced that exemption numerous times leading up to the fight.
When asked about the topic of performance-enhancing drugs during a pre-fight international conference call, Lesnar responded, "I'm a white boy and I'm jacked. Deal with it."