Evans -- who was born in Boston -- is one of the most famous Patriots celebrity fans. He's been to multiple Super Bowls and has hung out with Pats owner Robert Kraft.

But, the "Captain America" actor is also VERY anti-Donald Trump and told the Hollywood Reporter it would be very difficult to continue rooting for Tom Brady if TB12 is still supporting POTUS.

Remember, Tom publicly praised Trump back in the day -- and even rocked a "Make America Great Again" hat in his Patriots locker during Trump's presidential campaign.

But now, Evans says enough is enough ... and he doesn't think he can continue to root for Tom unless he disavows the Commander in Chief.

"I really hope he's not a Trump supporter," Evans said.

"I'm just hoping he's one of those guys that maybe supported him and now regrets it. Maybe he thought it was going to be different -- and even that bothers me -- but maybe there's a chance now he just thinks Trump's an absolute dumb sh*t, which he is."

"If he doesn't, if he's still on that Trump train, I might have to cut ties. It's really tough."

Evans continued ... "I think maybe a couple of years ago I might have tried to pull some, like, mental gymnastics to compartmentalize, but I don't know if I can anymore. So I'm just hoping he's woken up."

The good news for Chris ... Tom has pulled back his public support for Trump significantly over the past 2 years.

In fact, the QB missed a championship visit to Trump's White House in 2017 -- and still hasn't said whether he'll go if the Pats decide to make the trip for their latest S.B. win.

Tom has also said his wife, Gisele -- a big Trump critic -- has forbid him from talking about politics publicly anymore.

So, fact of the matter is no one REALLY knows how Brady feels about the President right now ... which is clearly bothering Evans.