UFC President Dana White has raised questions over Conor McGregor's motivation to return to competitive mixed martial arts.
McGregor has not fought for the UFC since he beat Eddie Alvarez to claim the lightweight belt in November 2016.
"Conor might never fight again," White said. "He made $100 million [from his fight against Floyd Mayweather].
"I've got guys who made less than that who are lawyers and went to school their whole lives and quit working."
"When you go to school your whole life to be a lawyer, and you're a good lawyer, and you make a few bucks and you're done? The guy's sitting home every day watching cartoons or whatever he's doing. I don't know."
"These guys make money and that's it. Fighting is the worst. Fighting is the worst. Try to get up and get punched in the face every day when you have $100 million in the bank. Money changes everything with a lot of people."
White has confirmed that he is in negotiations with McGregor over a new UFC contract but has dismissed suggestions that he will offer the fighter a stake in the company as an incentive to remain in the sport.
"If Conor wants to fight again, absolutely we want Conor to come fight, but if Conor walks away and doesn't ever want to fight again, it's part of the game," White told journalists at a media briefing at UFC headquarters in Las Vegas.
"Right now with him, it's not about defend or vacate. We're working on a new deal right now with him. We've got to work out this new deal."
McGregor was involved in a scuffle after he entered the octagon following a bout involving his teammate Charlie Ward in November
McGregor was involved in a scuffle after he entered the octagon following a bout involving his teammate Charlie Ward in November
McGregor, 29, was linked with a return to the UFC before the end of 2017 but his involvement in UFC219 was scrapped after the Dubliner jumped into the cage during a recent Bellator promotion and shoved a referee.
McGregor subsequently apologised for the incident but White has expressed his concern over the behaviour of the fighter and compared him to former Light Heavyweight champion Jon Jones, who was stripped of the title for a third time after failing a drug test at the weigh-in for his fight against Daniel Cormier in September.
"The other thing with the Bellator thing, he's a young rich kid who is a god in Ireland," White said of McGregor.
"That's not the healthiest environment either. I don't know if you remember in the beginning with Jon Jones. I'd go, 'There was no doubt the guy's talented, but he's young and rich and he's the king of the world now. Hopefully he can keep it together.' That was way before any of the crazy [stuff] started happening. And there it is, and it happens.
"What's weird is that it happens more in this sport, in the fighting business, than in any other sport."