The fight, the third episode of the McGregor-Poirier rivalry, was stopped towards the end of the first round after a bloody McGregor missed a punch and, taking a step back, twisted his leg in a shocking way.

Poirier then pounced on the sore McGregor with a series of punches and elbows until the Irishman was saved by the bell in the ring of the T-Mobile Arena.

“This guy was saying he was going to assassinate me and kill me. That I was going to get out of here in a coffin,” recalled Poirier, who was declared the winner by technical knockout. “You don't talk to people like that. I hope this guy gets home safely to his beautiful family."

Promoters later said McGregor suffered the injury to his lower tibia and was expected to undergo surgery on Sunday.

This fight, to five rounds, was to resolve the tie between McGregor, former champion of two categories of the Ultimate Fighting Championship (UFC), and his eternal rival Poirier.

In an interview inside the Octagon while waiting to be removed on a stretcher, McGregor said he was winning the fight when the accident occurred.

“He was boxing his bleeding head, kicking his bleeding leg. This is not over,” said McGregor, who has only had one win in the last four and a half years.

In 2014, McGregor knocked out Poirier in less than two minutes and in January the American got his revenge with a second-round knockout.

For the first time since the start of the pandemic, full capacity was allowed for a UFC fight in Las Vegas.

Among the public was former President Trump, who was booed by one part of the public while another chanted “USA” (United States).

Poirier's record reached 28 wins and 6 losses while McGregor's fell to 22-6.

Promoter Dana White said he hoped there would be a fourth fight between the two. "You can't let a fight end like this," he said.