McGregor weighed in three-and-a-half pounds heavier than Mayweather on Friday night ahead of his first professional bout, coming against one of boxing's all-time greats.
As of Saturday, four separate bets of $1 million or more had been placed on Mayweather to win.
Stephen Espinoza, the head of cable network Showtime Sports which is selling the fight on pay-per-view in the USA, said surveys had shown that fans were not deterred by predictions of a mismatch.
The Nevada State Athletic Commission, however, doesn't have the same concerns, because it views McGregor's physical attributes as a means to balance out the wide gap in boxing experience.
"Their response nearly universally was 'We don't care if it's a mismatch. if there's a.01 (percent) chance that something incredible could happen, we need to watch it'".
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But while McGregor, a long-odds underdog, has attracted most wagers, the majority of the money is on Mayweather.
"And that's why they're going to watch it".
Meanwhile, Conor McGregor's guaranteed minimum purse for tonight is $30 million.
Fans all over the world have taken to social media to show their support, but closer to home, a stunning tribute has been made in honour of the fight.
Both Mayweather and McGregor have spent large parts of the build-up to the fight trash-talking, with an ill-tempered global promotional tour laced with expletives, repeated homophobic slurs and allegations of racist language. Later in 2015, actor and Boston native Mark Wahlberg said he wanted to make a movie with McGregor. -Conor McGregor fight goes down, much of the SC football team will be together for it. He's not a bull in a china shop by any stretch of the imagination, but if his only chance according to the experts is to bum rush Mayweather and catch him early, will he change his strategy and go for it all?