Terence "Bud" Crawford‘s retirement this week shocked many, but not Shawn Porter … ’cause he tells TMZ Sports the boxing champion had been talking about hanging up the gloves for “a long time.”

In fact, Porter says Crawford began talking about the end of his boxing career just before their 2021 fight at the Mandalay Bay Resort & Casino in Las Vegas.

“I knew once he fought Canelo [Alvarez], he felt like there was nothin’ left for him,” Porter said.

“This is my first time saying — I never told anyone — that this is something that he’s been thinking about doing for a long time, wanting to do for a long time, but he knew that he had a little bit more to do.”

Porter — who retired after their 2021 fight — says boxers don’t just walk away on a whim or out of emotion … it’s a “calculated” decision that comes only when the time is right.

When it comes to the Mount Rushmore of boxing … Porter said Crawford is up there with Oleksandr Usyk in that era of the sport.

“To get it done despite all of these things coming at him … he did it.”