The move comes less than 24 hours after Tillman gave up six runs in 1 1/3 innings against the Kansas City Royals on Thursday night, leaving him at 1-5 with a 10.46 ERA.
After the game, he said: "I'm just not getting it done. It's not good right now. I've got to make better pitches."
In his previous start, Tillman gave up seven runs in one inning against the Angels.
Tillman signed a $3 million, one-year contract with the Orioles during the offseason after going 1-7 with a 7.84 ERA in 2017.
The 30-year-old has a 74-60 career record and was 16-6 in 2016.
Tillman will be replaced on the roster by right-handed reliever Jimmy Yacabonis, who was recalled from Triple-A Norfolk.