Conor McGregor has been branded "a snake" following a verbal altercation with replacement opponent Rafael Dos Anjos.
Dos Anjos weighed in on Friday as an insurance policy against either McGregor or Dustin Poirier suffering an injury before their trilogy fight this weekend.
All three lightweights scaled 156lb within 20 minutes of the weigh-in window opening before McGregor and Dos Anjos came together backstage.
Former lightweight champion Dos Anjos tweeted: "Conor you’re such a snake, sneaking from behind and playing tough. Soon or later we will finish business. I’m not like the guys you play around with."
McGregor and Dos Anjos were due to fight for the lightweight title in 2016 but the Brazilian pulled out injured with McGregor going on to lose to replacement opponent Nate Diaz.
McGregor has been riled since arriving in Las Vegas on Wednesday as he bids to avenge his January defeat by Poirier.
The Dubliner was stopped in the second round of the rivals' rematch, seven years after he himself knocked out Poirier in their first meeting.
And he vowed to "kill" the American when the cage door slams shut.
“Every shot I have thrown in this camp is a kill shot, so that’s it,” he said.
“I’m going to kill this man; just a slaughter and a play with a scared little boy.
“He’s fighting scared like he always does, like they always do against me, so now I’m going to play with the little boy, play with me food, and then just devour it.”
McGregor was also agitated at Thursday's press conference where he threw bottles of Dustin Poirier's hot sauce into the crowd before talking trash about his wife Jolie.
Poirier laughed off the insults, however, claiming: "For me the aura is not there anymore. I see a man I've defeated and one I'll defeat again."
McGregor then kicked out at his opponent as they faced off for the penultimate time before the first bell.
Dos Anjos, meanwhile, has won four and lost four of his eight bouts since his postponed clash with McGregor.
He lost his 155lb to Eddie Alvarez who in turn was stopped by McGregor. Dos Anjos also flirted with welterweight before dropping back down to defeat Paul Felder earlier this year.
He traded insults with McGregor this week when a report emerged that he would be the replacement opponent.
"Put Dos Anjos in at the same time," McGregor tweeted before Dos Anjos replied by questioning why his rival was tweeting in the early hours, saying: "Alcoholic [sic] hallucinosis from drinking cheap whiskey until 3:39am."
And while he is almost certain not to be fighting tomorrow night, he may be pitted against the loser while the victor marches on towards a title shot against Charles Oliveira.
