Brian Urlacher -- Opens Hollywood Baller Gym ... For Badass Athletes Only!

Brian Urlacher already has a spot to get into game shape if the Dallas Cowboys want him -- TMZ Sports has learned he's teaming up with Jay Glazer to start a high-end fitness center for pro athletes and Hollywood's elite.

Urlacher and Glazer -- pals from working together at FOX Sports -- are opening a gym called Unbreakable Performance on the Sunset Strip ... a prime location for catering to clients like Jerry Ferrara, Armie Hammer, and Marcedes Lewis.

The Cowboys are reportedly talking about luring Brian out of retirement ... but for now he's focused on the biz side of the gym. We're told Glazer will be a little more hands-on, doing personal MMA training with anyone who can hang -- as he's done with Clay Matthews and Forest Whitaker.

The gym is about 3500 sq ft split into 3 areas -- MMA training, high performance training ... and a freakin' mini football field, complete with artificial turf!!

Weekend warriors need not apply ... we're told Unbreakable will be strictly for ballers willing (and able) to pay premium rates for personal training.

Glazer & Urlacher -- like a modern day Hans and Franz ... with actual muscles.