Travis Frederick -- the Dallas Cowboys star center with Hall of Fame potential -- shockingly announced his retirement Monday ... this just 2 years after he battled a serious disease.
The 29-year-old fought through Guillain-Barre Syndrome -- a rare disorder that weakens the immune system -- in 2018 ... and the disease affected him so badly, he missed all of Dallas' games that year.
But the 6'4", 320-pound O-lineman returned to start all of the Cowboys' 16 games in 2019 ... and was even selected to the Pro Bowl.
Travis said in a statement Monday, however, he felt like his play had dipped .