The Irishman sustained a nasty-looking break to the lower tibia in his left shin with just seconds left in a wild first round at T-Mobile Arena in Las Vegas and is expected to undergo surgery on Sunday morning, according to UFC president Dana White.
McGregor’s ankle gave way in sickening, freak fashion as he stumbled backwards awkwardly after both men had missed with attempted strikes from close range, with the severe damage becoming apparent only after the horn had sounded, with ‘Notorious’ sitting with his back against the octagon and the lightweight bout quickly waved off as he received swift medical attention.
The doctor’s stoppage means Poirier has now won back-to-back fights against McGregor, leading their heated rivalry 2-1 following his shock stoppage win at UFC 257 in Abu Dhabi in January. He lost their first fight at featherweight at UFC 178 in 2014 within 106 seconds.
32-year-old McGregor - whose future in the UFC may now be called into real question with a lengthy lay-off ahead and three high-profile defeats in his last four fights - was behind on all three judges’ scorecards at the time of the stoppage on Saturday, with an attempted early guillotine on Poirier backfiring after McGregor had initially tried to inflict damage with some effective early low leg kicks - just as Poirier had done to him back in January before forcing a stoppage with a barrage of second-round punches.
Poirier - who had tried unsuccessfully for an early takedown himself - quickly escaped and had the upper hand thereafter, raining down heavy blows and elbows as the pair grappled against the cage during a frantic round, with blood visible around McGregor’s mouth and left ear.
The duo then got back to their feet, looking to trade powerful strikes at close range before the freak injury occurred.
Tempers flared between the bitter rivals again after the enforced stoppage, even with McGregor receiving treatment on the canvas and having his damaged leg placed in a protective brace as he was stretchered out of the octagon and away to hospital.
Poirier - who called his opponent a “dirtbag” - said that he thought McGregor had fractured his leg during an earlier exchange.
“I felt something, for sure,” he said.
“He fractured it on one of the kicks at the beginning of the fight, and then he broke it.”
He later said: “You never want to get a win that way, but what happened was the result of checking a kick.
“I’m more than sure of it. He got what he had coming to him. Karma is a mirror.”
Before he was taken away, a feisty McGregor - who denied that claim about an early fracture - bellowed during an utterly surreal interview with Joe Rogan: “This is not over. If I have to take it outside, let’s take it outside.”
Asked how he felt the fight had been going before the injury, he said: “I was boxing the bleedin’ head off him, kicking the bleedin’ leg off him.
“Just the thing had separated, and I bleedin’ landed on the wonky leg like Anderson Silva that one time [against Chris Weidman at UFC 168 in 2013], something similar to that.
“It’s a mad business.”
White confirmed after the fight that he expected a fourth instalment between Poirier and McGregor when the latter’s injury has healed, while Poirier is now set for a title shot against Brazil’s UFC lightweight champion Charles Oliveira next.
“The fight didn’t get finished. You can’t have a fight finish that way,” White said.
“We’ll see how the whole thing plays out. I mean, who knows how long Conor is out? Poirier will do his thing until Conor is ready.
“It sucks, it’s brutal, it’s not the way you want to see fights end.
“Dustin Poirier will fight for the title and when Conor is healed and ready to go, you do the rematch, I guess.”
In the co-main event at UFC 264, Brazil’s Gilbert Burns put himself quickly back in contention for another shot at dominant welterweight champion Kamaru Usman with a unanimous decision win over Stephen ‘Wonderboy’ Thompson.
Australia’s Tui Tuivasa knocked out former NFL star Greg Hardy inside the first round of a heavyweight contest before straddling the octagon and drinking beer from his shoe in celebration, while Irene Aldana dominated Yana Kunitskaya in a bloody women’s bantamweight showdown.
‘Sugar’ Sean O’Malley earlier delivered an emphatic one-sided beatdown of brave replacement opponent Kris Moutinho, while on the prelim card Max Griffin earned a career-best win over the legendary Carlos Condit, Michel Pereira outpointed Niko Price after a dramatic affair, Ryan Hall was stopped in the first round by Ilia Topuria and South Africa’s Dricus Du Plessis knocked out Trevin Giles on his US debut.
In the early prelims, Jennifer Maia earned a decision over Jessica Eye, Brad Tavares beat Omari Akhmedov and Kazakhstan’s Zhalgas Zhumagulov executed an incredible standing guillotine choke to submit Jerome Rivera in the first round.