Tom -- who's fully backed AB on social media even after rape allegations -- went on WEEI's "The Greg Hill Show" on Monday morning and declined to throw his weight behind AB again.

"I do have a lot of personal feelings, none of which I really care to share," the QB said. "That is about it. It’s a difficult situation. That’s kind of how I feel."

Of course, Tom was singing a very different tune earlier this month ... he was reportedly "one million percent" in on the Pats signing Brown -- and even reportedly offered the guy a room in the Boston-area mansion he shares with Gisele.

Tom also let AB into his personal gym ... and after Brown was cut from the Pats on Friday -- he left heart emojis on AB's Instagram post.

So, what happened to 'cause Brady to change his public gears? Unclear exactly ... but it seems like a safe bet to assume it had something to do with Brown's weekend attack on Kraft.

In a Twitter rant Sunday morning, Brown brought up Kraft's famous solicitation case, writing, "Kraft got caught in the parlor AB speculations fired different strokes different folks clearly."

The New England owner obviously didn't love the move ... because ESPN's Adam Schefter reported there's no way AB is getting his guaranteed money from the Pats now.

As for Brown, he continued to attack a lot of people on social media ... going after his ex-teammate, Ben Roethlisberger, and TV personality Shannon Sharpe.