Willis was trying to make a comeback with the Orioles, his fifth organization since the beginning of the 2010 season, through a turbulent season at Triple-A Norfolk that included struggles on and off the mound.
The Orioles announced Willis' retirement late Monday afternoon, and a tweet by Willis Monday indicated he had left the game.
"I'm deeply thankful for everything the game has done for me and I will always remember the great people I met along the way as well," Willis tweeted.
The Orioles signed Willis during
That triggered a public rift between the Orioles and Willis, whose agent said he was given permission to leave the team. Eventually, the sides reconciled, and Willis was given the opportunity to pitch as a starter again.
He worked his way back through extended spring training games, but made just one start for the Tides -- on Thursday -- lasting just 2 2/3 innings and allowing four runs on six hits.