Former UFC middleweight champion Anderson Silva has tested positive for anabolic steroids.

The Brazilian mixed martial arts fighter, who made a comeback from a leg break against Nick Diaz at the weekend, is regarded as one of the greatest of all-time.

Diaz also tested positive for marijuana, for the third time in his career.

Both fighters face possible bans and fines.

In a statement the UFC said: "On Feb. 3, 2015, the UFC organization was notified by the NSAC that Anderson Silva tested positive for drostanolone metabolites on his Jan. 9 out of competition drug test.

"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."

Earlier this month, news broke that light heavyweight champion Jon Jones tested positive for cocaine.