Charlamagne Tha God To Iman Shumpert -- Your New Song Is Garbage!

MTV star Charlamagne Tha God has a message for Cavs star Iman Shumpert ... back away from the mic slowly ... telling TMZ Sports he's heard Shumpert's new rap song, and it's totally garbage.

You might remember ... the last time Iman stepped in the studio it was to record a diss track aimed at the radio host, who Shumpert labeled as a hater for blasting his rap skills on "The Breakfast Club."

Shumpert's latest track -- a motivational song dedicated to the Cavaliers' playoff run called "The Offs" -- dropped yesterday and Charlamagne says although Shumpert's changed teams, his rap skills haven't changed at all.

"It's garbage. He needs to focus on his defense and not his rapping."

It gets worse ... Charlamagne says he questions Shumpert's focus -- and wants to know why he's making terrible rap songs when Cleveland is still 10 wins away from a championship.

"LeBron doesn't even tweet in the playoffs, and he's making rap songs!? The best motivation he could provide for his team is getting in the gym."

Ouch.