Conor McGregor suffered his second consecutive defeat to Dustin Poirier after breaking his leg at UFC 264 in Las Vegas on Saturday night.
Before the end of the first round McGregor's ankle rolled as he made a step backwards and the fight was stopped by doctors.
"This is not over," McGregor said.
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"If I have to take it outside, let's take it outside," he said as he was interviewed while sat on the canvas with his ankle strapped in a protective cast, before being stretchered away.
Dana White said after the fight that McGregor had broken the lower tibia in his left shin.
McGregor beat Poirier in 2014 before losing to the American in January. Defeat in the trilogy fight means McGregor now has a 1-3 record in UFC since 2016.
Victory for Poirier means he has the chance to reclaim the lightweight told he held in 2019 before losing to Khabib Nurmagomedov.
White said McGregor would have surgery in a Las Vegas hospital on Sunday morning and there are now doubts over whether the Irishman will return to the sport or move into boxing.
McGregor netted around $140m after a boxing match with Floyd Mayweather in August 2017.
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