Former UFC middleweight champion Anderson Silva and Nick Diaz both tested positive for illegal substances. The announcement came after the two fought each other in a pay-per view event over the weekend in Las Vegas. 

Silva failed an out-of-competition test Jan. 9 after testing positive for Drostanolone metabolites and another steroid. The 39-year-old Brazilian is considered to be the greatest mixed martial artist in the sport's history. 

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

Silva defeated Diaz by a wide decision, winning every round on two of the three judges' scorecards. It marked the first fight for Diaz since breaking his lower left leg 13 months ago.

In a brief statement, the UFC said it was "disappointed to learn of these initial 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," the UFC's statement added. "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 won 10 consecutive title defenses over seven years as the UFC's 185-pound champion until losing his belt to Chris Weidman in July 2013 and breaking his leg in the rematch.

Yahoo! Sports first reported the two fighters' failed drug tests. Both will face a disciplinary hearing before the Nevada commission Feb. 17, and their licenses will likely be suspended.

Silva is facing a nine-month suspension for his first failed drug test.

Diaz has tested positive for marijuana twice in his career, in 2007 and 2012. Diaz faces a lengthy suspension after returning from a 22-month self-imposed suspension to take on Silva.

The Associated Press contributed to this report