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Probably safe to assume Le'Veon Bell ain't coming back to the Steelers this week ... 'cause dude seems pretty busy livin' it up in Miami -- HITTING THE CLUB UNTIL EARLY TUESDAY MORNING!!

TMZ Sports has learned the star running back partied it up at Rockwell in South Beach ... and wasn't shy about it -- kickin' back at the DJ booth and taking pics with clubgoers.

We're told the Pittsburgh RB got there around midnight Monday and didn't leave until the wee hours of the morning Tuesday. He also partied at Gold Rush Cabaret Saturday night with friends.

Sources say he did look to be in great shape ... so at least there's that, Pittsburgh fans.

ICYMI ... Bell's been a no-show at Steelers practices AND at Sunday's game against the Browns as he continues to look for a mega deal from the team.

The Steelers are hosting the Kansas City Chiefs in Pittsburgh on Sunday. No word if Bell plans to be there. Hell, he might still be in Florida for all we know.

By the way ... this ain't the first time Bell's partied the night away instead of practicing with his teammates -- remember when he slapped all that butt at the booty club during training camp!?