Interim UFC light heavyweight champion Jon Jones has been pulled from his title unification bout against Daniel Cormier at UFC 200 on Saturday, after the U.S. Anti-Doping Agency informed Jones of a potential doping violation on Wednesday.
UFC president Dana White announced the move during an impromptu news conference at MGM Grand Hotel.
Jones tested positive for a banned substance in an out-of-competition sample taken June 16 by USADA, said Jeff Novitzky, UFC's vice president of athlete health and performance. USADA administers the UFC's anti-drug policy.
A heavyweight fight between Brock Lesnar and Mark Hunt will now headline UFC 200, which takes place on Saturday at T-Mobile Arena.
Jones has the right to appeal any positive test. He has never tested positive for performance-enhancing drugs, but did test positive for traces of cocaine prior to a fight against Cormier in January 2015.
Jones also served a suspension from April to October after his involvement in a hit-and-run accident.
Under the UFC's anti-doping program, which is administered by USADA and went into effect last July, a positive test for a performance-enhancing drug carries a standard 2-year suspension.
White said he'd like to find Cormier, the defending light heavyweight champion, a new opponent, but that would be difficult given the timing.
Cormier, who appeared next to White during the news conference, said he'd put in the work and would accept a new fight if the UFC could find one that "made sense."