The United States Anti-Doping Agency (USADA) 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 for the first time since December 2011 to defeat Mark Hunt via decision. The pro wrestling star remains under contract with WWE and 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 at UFC 200 on July 9 in Las Vegas.
"The UFC organization was notified today that [USADA] has informed Brock Lesnar of a potential anti-doping violation stemming from an out-of-competition sample collection on June 28," the statement said. "USADA received the testing results from the June 28 sample collection from the [World Anti-Doping Agency]-accredited UCLA Olympic Analytical Laboratory on the evening of July 14."
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.
The NSAC is already 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 due to 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 is also unknown at this time what the potential doping violation is for a banned substance or a banned methodology.
It is standard procedure for USADA to not immediately divulge the cause of the potential doping violation.
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. Due to the unique circumstances of Lesnar's return and his contract situation with the 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. In an interview with MMA Fighting on Friday, Hunt said he has asked UFC officials for half of Lesnar's $2.5 million purse or to be released from his contract effective immediately.
"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 told MMA Fighting that he has yet to hear from UFC.
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."
