Herschel Walker: Shut Up Mitt Romney ... You're a Loser!

Herschel Walker's got his old boss' back -- ripping Mitt Romney for his anti-Trump speech this morning ... essentially calling the guy a loser.

Walker has been an extremely vocal supporter of his 'Celebrity Apprentice' boss -- previously telling TMZ Sports he believes Trump will "save America."

Now, with Mitt Romney blasting Trump this morning as a "phoney" who is dangerous for the country -- and John McCain also denouncing him -- Walker went to bat for Donald with a new statement:

"McCain and Romney lost the playoffs years ago yet they want to talk about someone getting ready for the Super Bowl ... Think about that."