Bruce Willis Gambles at Craps Table in Vegas on Eve of Mayweather/McGregor Fight

Bruce Willis is betting on himself in Vegas on the eve of the Mayweather/McGregor fight.

Bruce was playing craps at the MGM Grand Friday night ... he's in town to catch the fight.

Check out the photo ... it's interesting he's just a dude at the table ... not attracting much attention.

There's a lotta loot riding on this fight, and that trumps any celeb siting.