Rob Gronkowski Squats Camille Kostek at Nightclub Bash

He may be retired, but Rob Gronkowski's still training like a pro ... even while partying at the club!

The ex-NFL superstar was celebrating his girlfriend, Camille Kostek, being selected as a cover model for the new Sports Illustrated Swimsuit Edition at the Wall Lounge in Miami.

The party was crazy -- a bunch of the S.I. models turned up to turn up ... and when they displayed Camille's cover on the big wall, Rob and CK started dancing their faces off.

At one point, Gronk put CK on his back and began doing deep squats -- BECAUSE HE'S A BEAST AND HE'S ALWAYS LIFTING, BRO!!!

Before the club, a bunch of the models hit up Irma's at W South Beach for a kickoff party. Some of the stars in attendance include UFC's Paige VanZant, Tyra Banks, model Veronica Pome’e and Hailey Clauson.

Congrats!