Anderson Silva
Anderson Silva reportedly failed a drug test the night of his fight. (Getty Images)

Former UFC middlewight champion Anderson Silva failed a second urine test administered the night of his UFC 183 bout against Nick Diaz in Las Vegas.

On Jan. 31, Silva's postfight samples came back positive for the steroid drostanolone, anti-anxiety medication Oxazepam and Temazepam, which is used to fight sleep deprivation, Nevada State Athletic Commission executive director Bob Bennett confirmed Tuesday, per ESPN.

Overall, Silva (34-6) provided three exams leading up to the fight. He tested positive for drostanolone and androstane on Jan. 9 before having a clean exam on Jan. 19, followed by another failed sample on Jan. 31.

"I have not taken any performance enhancing drugs," the 39-year-old Brazilian said in a statement released on Feb. 4 -- soon after his first positive test. "My stance on drugs is, and will always be, the same. I'm an advocate for a clean sport."

Silva could be facing a nine-month ban, which is what fighters face for failing their first banned substance. Bennett is unsure if Silva will face a lengthier suspension for failing multiple tests.

"I can't speak for the [NSAC] Chairman nor can I speak for the commissioners," Bennett told ESPN. "But something I find particularly concerning is that he tested positive on Jan. 9th and then he tested negative on Jan. 19th. If he took this orally, it only stays in your system 5-to-7 days.

"So, obviously, he used it sometime around Jan. 9th and then he used it shortly before the night of the fight. Whether the commission finds this egregious -- that he tested positive twice out of three times -- is up to them. I certainly find it concerning and unacceptable. It gives an unfair advantage to the person on that. God forbid, a serious injury were to occur to an opponent when someone is on something."