Nate Diaz's fight against Jorge Masvidal at UFC 244 next month is back on, after the governing body said he had not failed a doping test.
On Thursday the American said the bout was off, saying that he had been told he tested with "elevated levels".
But UFC said in a statement: "Mr Diaz has not committed an anti-doping policy violation, has not been provisionally suspended and is not subject to any sanctions."
Diaz, 34, had denied any wrongdoing.
On Thursday he said: "I only take whole food or natural food supplements. I'm not going to have my name tainted as a cheater."
UFC 244 takes place on 2 November in New York.
UFC said that in an out of competition test carried out by the US Anti-Doping Authority (Usada) on 24 October, LGD-4033 was found in small quantities in Diaz's sample.
LGD-4033 is a substance which can be used to increase testosterone.
However UFC said that the amount found in Diaz's sample was "roughly 10,000 times lower than one LGD-4033 therapeutic dose".
Further tests "confirmed that two bottles of the same organic, vegan, plant-based daily multivitamin that Mr Diaz was using were each contaminated with LGD-4033, which the evidence supports resulted in Mr. Diaz's positive sample.
"UFC has been informed by independent experts who have determined that there is unequivocally no appreciable performance enhancing or therapeutic benefit from the significantly limited amount of LGD-4033 that may be present in his system."
Usada added: "Following Mr Diaz's public comments on Thursday we can confirm that he has not been sanctioned or provisionally suspended by Usada."