Floyd Mayweather says Justin Bieber turning traitor on him is the last thing on his mind on the eve of THE fight ... but he's still throwing jabs at his former BFF.

Floyd sat down with 'Hollywood Unlocked' and talked about the video TMZ posted of Justin -- saying he didn't think Floyd would KO Conor McGregor. The champ tried like hell to keep it above belt, but his disdain came spilling out when he dismissed Bieber as a "pop star."

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As we reported, Floyd was screaming mad about JB's words and his IG unfollowing. He might cool down eventually.

But not yet.

MY PREDICTION ...
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