"Each day I faced a struggle: I could no longer perform at my highest level," Frederick said. "Playing 'well' is not what I expect of myself and is not what my teammates deserve."
"Because of this, I know my days as a football player are done."
Travis says his time away from the Cowboys, fighting off his illness two seasons ago, opened his eyes to life after football ... and made his decision this week easier.
"Facing the potential end of my career because of my illness forced me to imagine life after football," Travis said. "I had to prepare for my career potentially ending ... After months of contemplation, I not only accepted that moment, but I also surprisingly found myself welcoming the moment."
Travis was the Cowboys' first-round pick in the 2013 NFL Draft ... and he went on to have a monster career, being selected to FIVE Pro Bowls in six seasons.
The offensive lineman signed a 6-year, $56 MILLION contract with the Cowboys back in 2016 that made him the NFL's highest-paid center.