An eye-popping $1.2 million bet is among a flurry of big-money wagers on Floyd Mayweather as the welterweight champion prepares to take on mixed martial arts star Conor McGregor, bookmakers reported on Friday.

As Mayweather and McGregor readied to face each other at a weigh-in later Friday, Las Vegas bookmakers were reporting a surge in betting on Saturday's cross-combat sports showdown at the T-Mobile Arena.

Bookmakers have said the total amount gambled on the bout will make it the most bet-upon fight in Las Vegas history.

William Hill US reported that the flood of bets in the past 24 hours included a punter who strolled into a sports book and handed over $1.2 million in cash on Mayweather, a 1/5 favourite. If Mayweather wins, the bet will earn around $240,000.

"It's going to be the biggest fight handle ever. Period," William Hill US director of trading Nick Bogdanovich said. "Whether it's boxing, gladiators or Game of Thrones."

William Hill said another gambler had staked $300,000 on the outcome in Mayweather's favour.

The MGM sportsbook also took a $1 million bet on Mayweather on Thursday, according to ESPN. The bet would net around $182,000 in profits.

Vegas bookmakers say that while the majority of bets on the fight have been placed on McGregor, a 5-1 underdog, most of the total 'handle' or betting pool has been placed on Mayweather.

Bogdanovich told AFP that bets on McGregor were outstripping wagers on Mayweather by a ratio of 17 to 1.

Bookmakers face multi-million-dollar losses if McGregor stuns the boxing world and upsets Mayweather on Saturday.

William Hill said the biggest bet it had received on McGregor so far came on July 24, when a bettor staked $150,000 on the Irishman, setting up a potential $662,500 windfall if Mayweather loses.

Most experts say McGregor, who has never fought in a professional boxing contest, has next to no chance against Mayweather, the 40-year-old former welterweight star who retired in 2015 with a 49-0 record.

Mike Tyson's former trainer Teddy Atlas was one of the latest voices to write off McGregor's chances of springing a surprise.

"It's going to be like walking through a really bad neighbourhood late at night," Atlas said of McGregor. "He's going to get mugged."

Source: AFP