Travis Kelce's playing days may be coming to an end soon, but Henry Winkler is making it clear he thinks the NFL star's acting career is just getting started ... telling TMZ Sports he loved the dude in "Grotesquerie."

We caught up with Henry out in Los Angeles this week ... and he had nothing but praise for the way Kelce played a flirty ex-stripper in his son Max Winkler's new horror drama series.

The Fonz said Kelce gave off a "warm and professional" vibe during the show, while calling the footballer's portrayal of Ed Lachlan "great."

"I don't know if he has award-winning -- no one knows that," Henry said. "What I do know is that he really did a great job."

Seems Henry thinks his son would agree ... explaining his 41-year-old boy told him Kelce was "wonderful" on set.

The "Happy Days" star, though, was not as complimentary of Kelce's teammate, Patrick Mahomes ... as he said the quarterback is still ducking his chicken dinner invitation.