The potential violation stems from an out-of-competition drug test submitted on April 25. As is customary under the UFC's anti-doping program, no further details have been revealed.

"We're working very closely with [UFC Vice President of Athlete Health and Performance] Jeff Novitzky, the UFC and USADA," said Werdum's manager, Ali Abedalaziz. "I'm very confident this situation will be resolved."

Werdum, 40, has never failed a drug test in his career, which dates to 2002.

News of the potential violation comes just one day after MMAFighting.com reported the UFC was close to finalizing a bout between Werdum (23-8-1) and Aleksei Oleinik to headline its first event in Russia, on Sept. 15.

Werdum is coming off an upset knockout loss to Alexander Volkov in March. He surrendered his UFC title to current champion Stipe Miocic in May 2016, and he has set his sights on reclaiming the belt. He is 3-2 since the Miocic loss.

Originally from Porto Alegre, Brazil, Werdum trains out of Kings MMA in Southern California.