Conor McGregor was sensationally defeated for the second time in two fights after breaking his leg at UFC 264 on Saturday night in Las Vegas.
The Irishman, 32, was stopped after the first round against former interim lightweight champion Dustin Poirier.
Replays showed his ankle rolling over as he stepped backwards seconds before the end of the round and the fight was stopped by doctors, handing Poirier a second straight win in their trilogy.
“This is not over,” McGregor said.
“If I have to take it outside, let’s take it outside,” he added as he was interviewed while sat on the canvas with his ankle strapped in a protective cast, before being taken out of the ring on a stretcher.
UFC president Dana White said after the fight that McGregor had broken the lower tibia in his left shin.
McGregor had defeated Poirier via first-round TKO at UFC 178 in 2014, but the American, also 32, evened the score with a second-round TKO at UFC 257 in January.
It meant the rivalry was perfectly poised heading into their trilogy bout in Las Vegas, and it was Poirier who emerged victorious in unfortunate circumstances.