Rob Gronkowski Gets Acting Advice From Ex-NFL Star Thomas Jones

Rob Gronkowski will NOT be successful transitioning from the NFL to Hollywood if he doesn't take it seriously ... so says ex-NFL star Thomas Jones -- who says the move is hard as hell!!!

Of course, TJ knows first-hand what it takes to go from on-the-field stud to on-the-screen star ... he spent 12 years in the league before becoming a respected actor.

And, he tells us the only way Gronk is going to have similar success is if he truly devotes himself.

"Just commit yourself to the industry, man," Jones says of his advice to the future Hall of Fame tight end ... "You can't really halfway do this. You have to really, really buy into it."

The reason? Jones says football players have to train themselves to be "inhumane" to be a beast on the field ... but acting requires more vulnerability.

In fact, Jones says he took acting classes for 4 YEARS to get that all down ... saying, "I took the craft seriously."

The good news for Gronk? Jones says the ex-Patriot will be a natural once he decides to put all his energy into it.