Nick Diaz punches Anderson Silva
Nick Diaz punches Anderson Silva of Brazil in their middleweight bout during the UFC 183 event at the MGM Grand Garden Arena on January 31, 2015, in Las Vegas Getty

UFC has been plunged into a drug scandal after main event fighters Anderson Silva and Nick Diaz both failed drug tests.

Silva made a triumphant return to the sport at Las Vegas's MGM Grand Arena on Saturday, Januray 31, when he defeated Diaz in a points victory at UFC 183.

But the fight has been overshadowed after Silva tested positive for anabolic steroids, while Diaz was positive when tested for marijuana.

The revelation was further complicated when it emerged Silva had provided a positive sample for drostanolone and androstane to the Nevada Athletic Commissionas as long ago as 9 January.

However, the sample was not returned until Tuesday, three days after the mixed martial arts fight.

Diaz's positive results for marijuana metabolites were the third of his career after failing tests in 2007 and 2012.

The Nevada state commission is likely to rule the fight a no-contest.

UFC statement

On February 3, 2015, the UFC organisation 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.