Silva denies doping, doctor says

— -- SAO PAULO -- The medical director of Brazil's governing body for mixed martial arts says he talked to Anderson Silva and the Brazilian fighter denied using steroids.

UFC said Tuesday the former middleweight champion tested positive in an out-of-competition test on Jan. 9. The announcement came just days after Silva beat Nick Diaz in Las Vegas in his return to the cage after breaking his lower left leg 13 months ago.

In an interview with a Brazilian radio station, Marcio Tannure said Silva told him he is "disappointed" and "upset" with the news that he tested positive.

Tannure told Radio Band News that Silva believes there was "contamination" or a "mistake by the laboratory" that handled his test.

The doctor said Silva will request his "B" sample be tested.

Silva, 39, had tested positive for the steroid drostanolone during a random out-of-competition test administered by the Nevada State Athletic Commission on Jan. 9. NSAC chairman Francisco Aguilar confirmed the positive test to ESPN.com's Brett Okamoto. ESPN.com obtained a copy of Silva's lab report, which indicates he also tested positive for a second steroid, androstane.

Silva (34-6) defeated Diaz via unanimous decision at UFC 183 at the MGM Grand Garden Arena. The NSAC said results of the prefight test were not available until Tuesday morning, which is why the fight was not canceled.

Additionally, Aguilar informed ESPN.com that Diaz (26-10) tested positive for marijuana metabolites during a postfight drug test. Aguilar said exact results were unavailable but confirmed Diaz's results were above the allowable limit of 150 nanograms per milliliter.

According to Aguilar, Silva was tested on Jan. 9, Jan. 19 and Jan. 31 -- all blood and urine tests. Results of the out-of-competition Jan. 19 test are currently unavailable.

Each fighter faces a potential fine and suspension. It marks the third marijuana-related offense for Diaz.

The NSAC's next scheduled meeting is Feb. 17. Silva and Diaz likely will be temporarily suspended at that time. Full disciplinary hearings will be scheduled for each.

The Associated Press and ESPN.com's Brett Okamoto contributed to this report.