Every blockbuster fight needs a big-time promoter ... and Floyd Mayweather tells TMZ Sports he's the guy for Justin Bieber's potential fight against Tom Cruise!!
As we previously reported ... there have been serious talks about setting up a fight between the 25-year-old singer and the 57-year-old movie superstar after Biebs playfully tweeted about wanting a piece of TC last month.
Dana White -- who was tagged in Bieber's initial post about the dream fight -- has said he'd be down to make it happen and predicts it would be the biggest fight in UFC history.