Fans descended onto the concourse at the T-Mobile Arena in Las Vegas after the Irishman tapped out in the Octagon last night.
Khabib Nurmagomedov put McGregor in a chokehold in the fourth round and within moments the fight was over.
However, the drama only escalated when the Russian climbed out of the cage into the crowd and unleashed himself onto McGregor’s coach Dillon Danis.
The focus quickly turned back to the Octagon as a member of Khabib’s team jumped into the ring and attacked McGregor, landing a punch on the back of his head.
Tensions continued to increase as the 18,000 fans started to leave the arena.
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Violent scenes unfolded in the concourse, according to videos widely shared on Twitter and Snapchat.
Crowds were chanting “ole, ole, ole, ole!” as a man, reportedly a McGregor fan, was seen taunting a crowd by jumping and giving them the middle finger.
Another man in a black t-shirt and trousers then tried to kick him in the face.
In retaliation the supposed McGregor fan wearing a white t-shirt spat back in his face.
Two groups of men then came to blows as they started shoving each other.
The reported McGregor fan was promptly knocked out by the man wearing black.
The crowd cheered as the man remained on the ground before bystanders stepped in to help the unconscious man off the floor.
At time of publishing it was not clear if any of the fans were arrested or if they had been identified.
Saturday night’s brawls have forced the Nevada State Athletic Commission to investigate what transpired.
The president of the UFC Dana White confirmed last night three members of Khabib’s team were arrested.
He said in a UFC 229 video from after the fight: “I spoke to Conor and he is okay.
“Three of Khabib’s guys were arrested and taken to jail. And God knows what the Nevada State Athletic Commission is going to do.
“I’ve heard both of their purses are being held now. This is a big deal.”
White later confirmed the three of the Russian’s party were released.
The commission have withheld Khabib’s £1.5million ($2million) pay-cheque but have given McGregor his £2.29million ($3million), as reported in The Sun.
It was a bitter end to one of the biggest fights in UFC history.