American Nate Diaz says will not fight at UFC 244 next week after suggesting he has failed a doping test.
In a post on Twitter he said he had been told he tested with "elevated levels" and although he did not give further details he said "you're all on steroids not me".
Diaz, 34, denied any wrongdoing, saying "I only take whole food or natural food supplements".
"I'm not going to have my name tainted as a cheater," he said.
Diaz is scheduled to fight Jorge Masvidal on 2 November in New York.
Masvidal responded on Twitter, saying he will "see" Diaz "on 2 November" and adding "I know your name is clean".