NFL Star Antonio Gates -- Shoots TV Show Cameo ... On Day Off

ANTONIO GATES IS BACK!!!

Not just because he's having one of the best seasons of his career, but he's also returning to "The League" ... and TMZ Sports has the footage.

The San Diego Chargers tight end used his day off from practice to come up to L.A. to shoot a cameo on the hilarious FXX show ... and he talked to us about the shoot on his way off the set.

Gates has been on the show before -- and was hilarious ... when he was confronted by one of the characters in a hot tub whose fantasy team had lost because Gates scored a TD.

So, does Antonio have a post-NFL career in Hollywood?? Check out the clip ... he's not exactly shooting down the idea.