Floyd Mayweather Jr admits he is taking a big risk fighting Conor McGregor but remains confident his "granite chin" will see him deal with everything the UFC star throws at him.

Mayweather will put his 49-0 record on the line in Las Vegas this weekend after opting to come out of retirement to face McGregor in a blockbuster fight that has caught the world's attention.

The American has long been favourite to come out of the bout with a victory given his experience and boxing know-how, but McGregor's unpredictability has seen many backing an upset.

Mayweather remains confident he has what it takes to preserve his undefeated record, though, and cited his battles with Manny Pacquiao, Saul 'Canelo' Alvarez and Shane Mosley as prime examples of his strong chin.

"I've been here so many times, I know what it takes in a fight of this magnitude," he told a media conference at the MGM Grand on Wednesday.

"He's a hell of a fighter, a stand-up guy, a tough competitor, this is not going to be an easy fight, there will be blood, sweat and tears.

"After 21 years I've been hit with everything and I'm still here.

"He's going to bring his best, it is not going to be easy, but remember Pacquiao got bombs, Canelo got bombs, Shane Mosley had bombs but I've got a granite chin.

"I'm taking a gamble, but it's a gamble worth taking."

Mayweather finished his complimentary speech with one final warning for McGregor, adding: "Remember, the same way you give it, you have to be able to take it.

"One thing I can do is fight. To be 49-0 it is obvious I am giving it, not receiving it."