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A bettor placed a huge wager on Floyd Mayweather Jr. on Thursday, and as a result, Mayweather is a slightly larger favorite to beat Conor McGregor on Saturday in Las Vegas' T-Mobile Arena.

ESPN.com's David Purdum reported the MGM sportsbook accepted a $1 million bet on Mayweather. The bettor placed the money when Mayweather was a 2-11 favorite, and his odds have since shifted to 1-6.

Purdum noted the $1 million bet would pay out almost $182,000 should Mayweather win.

ESPN.com's Darren Rovell reported the biggest bet so far was registered with William Hill. Somebody put $1.2 million on Mayweather, which would bring a $240,000 payout.

The gulf in odds is evidenced by the bets fans have made on the respective fighters. The Westgate SuperBook told Purdum the average bet for McGregor was $212, while fans were putting an average of $8,036 on Mayweather.

CBSSports.com's Brian Campbell reported McGregor's odds had been improving in recent weeks because of the volume of money placed on the UFC lightweight champion. According to OddsShark, McGregor is a 13-4 underdog. When betting opened in November for Mayweather vs. McGregor, McGregor was a 19-2 underdog, per OddsShark.