Former UFC middleweight champion Anderson Silva tested positive for Drostanolone metabolites in an Jan. 9 out-of-competition drug test ahead of his UFC 183 comeback fight against Nick Diaz, the UFC announced Tuesday.

Drostanolone is a common form of anabolic steroid.

The UFC released the following statement regarding Silva's failed test:

"On February 3, 2015, the UFC organization was notified by the Nevada State Athletic Commission that Anderson Silva tested positive for Drostanolone metabolites on his Jan. 9 out of competition drug test. UFC's understanding is that further testing will be conducted by the Commission to confirm these preliminary results. "Anderson Silva has been an amazing champion and a true ambassador of the sport of mixed martial arts and the UFC, in Brazil as well as around the world. UFC is disappointed to learn of these initial results. "The UFC has a strict, consistent policy against the use of any illegal and/or performance enhancing drugs, stimulants or masking agents by its athletes."

Silva, 39, defeated Diaz via unanimous decision on Jan. 31 in the main event of UFC 183. The fight was Silva's first since Dec. 2013, when Silva suffered a grisly -- and what at the time looked to be career-ending -- broken leg midway through the second round of his UFC 168 rematch against Chris Weidman.

A record-shattering UFC champion, Silva (34-6) is widely considered to be one of, if not the single greatest mixed martial artist of all-time, having won his first 16 fights inside the UFC in dramatic and often dazzling fashion.

MMA Fighting will continue to update this story as information becomes available.