Sylvester Stallone -- What's Good for Floyd Mayweather Jr. ... Is Great for 'Creed'

Floyd Mayweather won't be in 'Creed,' but his swag will be -- Sylvester Stallone tapped Floyd's favorite boxing glove company to be the official mitt of the movie.

Elvis Grant, CEO of of Grant Worldwide tells us Sly called him personally to request his company outfit all the fighters in the latest Rocky flick. It's no wonder Stallone reached out -- Mayweather uses Grant exclusively for his fights, and umm ... last we checked that guy's 48-0.

The only thing cooler than having your company's gear in a Rocky movie ... is being in the movie yourself -- and Grant got that too. He says Sly gave him a cameo.