"He literally loves playing in Houston," the Hall of Fame quarterback tells us. "He loves the city. He's involved in it a lot. But he definitely wants to win."

Watson, according to NFL Network's Ian Rapoport, is "extremely unhappy" with the Texans heading into this offseason ... reportedly upset over his lack of input so far in the hiring process of the team's new GM and head coach.

Now, many believe that could lead to a trade ... but when we spoke with Moon -- a close friend of Deshaun's -- the 64-year-old told us he's not expecting the QB to be dealt with anytime soon.

In fact, Moon tells us he's pretty confident 25-year-old Watson will still be under center in Houston in 2021.

"If they really sit down and listen to this guy, and listen to what his feelings are, they'll give him a lot of input into who that next head coach is going to be," Moon says.

"And if that happens, I think he'll be happy there."

The problem? Moon believes if Houston doesn't do that ... a trade request from Watson could then follow.

"This is a guy that comes from a Clemson program where he won a national championship, he lost another one in the championship, so he's used to winning football," Moon says, "and it just hasn't been that way for his team this past year and he sees them going in a downward slide."

If the Texans aren't able to keep Watson happy ... Moon says he believes a bunch of teams could be suitors for his services.