WWE superstar Mojo Rawley saw Rob Gronkowski call him out to TMZ Sports ... and he's got a message for the NFL star -- don't let your mouth write checks your ass can't cash!!!
Remember, just a few weeks ago Gronk said he'd consider inking a deal with the WWE just to get a crack at that "wimp" Mojo Rawley -- "I gotta go in that ring and whoop his ass!!!"
So, we hit up Mojo ... and man, HE'S TALKING SMACK!