The 33-year-old hung up his spikes in June 2022 ... but many thought he could eventually make a return -- considering he had already retired and unretired once before in his career.

But, after sitting out the entire 2022 season -- and, after his good buddy, Tom Brady, called it quits this offseason -- Gronk told Michael Babcock and Mojo Muhtadi he's officially done.

"There's no chance anymore," the former Buccaneers and Patriots tight end said of a possible comeback. "I'm happily retired."

Gronk, though, says he's still using his athleticism ... telling the guys he's actually picked up pickleball in retirement -- and, according to him, he's good at it!!

"I beat my brother, Chris, who plays with pros, and my other brother, Gordon, who plays with pros too!" he said. "And I beat 'em with an average Joe -- my other brother, Glenn G., was my partner!"

"So," he added, "I'm happily retired. I'm still competing, I'm still winning, so I don't even need to go back to football."

Gronk is also spending time at his alma mater, the Univ. of Arizona, where he's slated to be a team captain for the Wildcats' spring football game on April 15.

Gronk will face off with his bro, Chris, who will also be manning the team opposite of Rob's.