ESPN reports that Mayweather tried to place a $400,000 bet on the fight ending under 9.5 rounds at -200 odds (bet $200 to win $100).
Sources confirmed that the boxer went to the sportsbook at the Las Vegas M Resort on Saturday at 3:30 p.m PT with cash in hand.
Unfortunately for Mayweather, the agency didn't accept his bet. They were unsure on the legality of a boxer betting on specific details of his own fight.
He then simplified his bet to him winning by knockout, but became "pissed" when he had to wait long to place the bet. He decided to leave before putting any money down on the fight.
Mayweather seemingly confirmed the report after the match and revealed that he had someone else handle the bet on his behalf.
"I think that we bet 100 on 9.5," Mayweather said. "I gave my guy six figures to go bet. I have to make sure he bet because earlier today I went to the sportsbook to bet and they wouldn't let me bet."
Mayweather's prediction was spot on. The referee stopped the fight 1 minute, 5 seconds into the 10th round, with McGregor getting TKO'd.