On Thursday, Archangel Michael Fight Club, a Russian MMA gym, announced that one of their fighters, top light heavyweight prospect Ivan Shtyrkov (16-0-1), has parted ways with the UFC over a potential doping violation.

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“Russian fighter Ivan Shtyrkov (15-0-1) and the UFC have terminated the contract by agreement of the parties,” the gym announced on Instagram.

Shtyrkov, 31, signed with the UFC in March. The undefeated Russian behemoth was a highly touted signing, as he had competed in one of Russia’s top promotions, RCC, against increasingly talented opposition over the past several years.

The Russian 31-year-old has faced and defeated a bevy of notable opponents, including former UFC heavyweight champion Ricco Rodriguez, Jeff Monson, Antonio “Bigfoot” Silva, KSW heavyweight champion Phil de Fries, PFL contender Satoshi Ishii, and UFC veterans Fabiano Maldonado and Thiago Silva.

Shtyrkov was slated to take on Devin Clark at UFC St. Petersburg, but the fight was canceled due to a reported illness to Shtyrkov. In the wake of his gym’s announcement, which included a statement regarding a possible drug test failure for a substance for “gaining muscle mass,” some, including Clark himself, showed skepticism that the illness was to blame.

“The reason for the decision [to leave the UFC] is a possible disqualification of a fighter because of the prohibited substance pictogram for gaining muscle mass which was found in the doping test,” the gym said.

“The first test, taken immediately after signing the contract with the UFC, did not show any banned drugs in the body, but the result was atypical. The further opening of the “B” sample, which was analyzed in more detail, showed insignificant residues of one of the prohibited substances for weight gain. It is worth noting that after this Ivan had two more tests,” the post added.

Additionally, the gym announced that Shtyrkov will be exploring other promotions outside the UFC.

“Therefore, Ivan didn’t wait for the decision of the disciplinary commission and asked to release him from the contract in order to look for options to continue his career in other organizations.”

It is unknown at this time what substance Shtyrkov appeared to test positive for, nor is it known where Shtyrkov will land. Likely, the Russian finisher will end up in an organization in his homeland, perhaps returning to his longtime home of RCC.

Neither the UFC nor USADA have commented on Shtyrkov’s UFC status at this time.