Nate Diaz has cast doubt on his upcoming fight against Jorge Masvidal after suggesting he has failed a doping test ahead of UFC 244.
Diaz is scheduled to face Masvidal at Madison Square Garden on November 2 in his second fight since returning to MMA after a three-year break.
In a post on Twitter, which included the caption "You're all on steroids not me", Diaz claimed he had returned "elevated levels" in a pre-fight test.
"I'm not going to make it out to NYC for fight week next week because they say I tested with elevated levels that they say might be from some tainted supplements," wrote Diaz.
"I call false on that cause I only take whole food or natural supplements. I don't even eat meat."
UFC has yet to confirm if Diaz is cleared to fight in New York but Masvidal insists he is preparing as normal and believes his opponent his clean.
"I'll see you Nov 2. I know your name is clean," Masvidal wrote on Twitter.
Diaz challenged for the UFC lightweight title in 2012 but lost to Benson Henderson on a unanimous decision.
Diaz went on to face Conor McGregor in 2016 and became the first man to beat the Irishman in the UFC, before losing their rematch later that year.
The American took a three-year break from MMA after his defeat to McGregor but returned to the sport earlier this year at UFC 229, where he beat Anthony Pettis.
Masvidal, meanwhile, heads into UFC 244 on the back of wins over British fighter Darren Till and Ben Askren, who he defeated inside five seconds at UFC 239 - the fastest knockout in UFC history.