Lightweight Thiago Tavares tested positive for the anabolic steroid drostanolone following his Jan. 19 loss in Rio de Janeiro, UFC announced Wednesday on its website.
The promotion has suspended Tavares for nine months retroactive to the date of the UFC on FX 7 event. Tavares has been informed that he must pass a drug test upon completing his suspension.
Marc Ratner, who is the UFC vice president of regulatory affairs, confirmed Tavares' failed drug test with ESPN.com.
All 22 fighters who competed on the card were tested after the event. Everyone except Tavares tested negative for banned substances. Drostanolone is an anabolic steroid, most frequently seen in professional bodybuilding.
Shortly after the event, talk began circulating that a fighter had failed his postfight drug test. Much of the speculation centered on former UFC light heavyweight champion Vitor Belfort.
UFC addressed the matter in its official statement: "Zuffa wishes to clarify that Vitor Belfort's drug test results were negative and did not indicate the presence of any performance-enhancing drugs."
Tavares was knocked out in the first round by Khabib Nurmagomedov. He entered the bout on a two-fight win streak.
Information from ESPN.com MMA reporter Brett Okamoto contributed to this report.