Silva, the 39-year-old Brazilian widely considered the greatest mixed martial artist in the young sport's history, tested positive for Drostanolone metabolites and another steroid in an out-of-competition test Jan. 9.

Nick Diaz, his opponent at UFC 183 last Saturday, also tested positive for elevated levels of marijuana metabolites in results released Tuesday night by the Nevada Athletic Commission.

The UFC said the commission is doing further testing to confirm the results, but the stunning announcement casts a large shadow over Silva's impressive comeback from a badly broken leg last Saturday for a unanimous-decision victory over Diaz.

In a brief statement, the UFC said it was "disappointed to learn of these initial results."