Floyd Mayweather -- Warren Buffett Joins 'The Money Team!'

Screw 50 Cent, Floyd Mayweather has a more rich and powerful ally in his corner -- Warren Buffett ... and the two hung out together at Floyd's boxing gym in Vegas Tuesday.

TMZ Sports has the footage of Warren arriving to the location (where he was told he would have to WAIT because Floyd hadn't arrived yet).

But this video is GREAT ... with Warren telling us the ONE casino game he refuses to play when he's gambling in Sin City.

Warren wouldn't say why the two met up -- or how they became friends -- but Floyd later went to Instagram and wrote, "We talked about how we could turn a $100 million of my assets to $1 billion."

Hey Floyd ... feel free to SHARE that info. Thanks.