Michael Jackson's nephew says Drake should've left MJ's unreleased track off his new album ... because Michael wasn't ready for the world to hear it.
Drizzy's "Scorpion" hit Friday ... a track called "Don't Matter to Me" on the album samples an unheard Michael song that was recorded before "Thriller."
Rebbie Jackson's son, Austin Brown, was in Hollywood Friday and flat out says he's not OK with Drake using the unreleased Michael track. Austin believes if MJ didn't finish the song, Drake shouldn't have used it.
Brown does give Drake some props for his talent, but his overall message is clear -- don't touch the secret stuff.