Rapada, on the 15-day disabled list since May 21 with biceps tendinitis, made a Minor League rehabilitation appearance at Triple-A Toledo on Saturday night and felt well enough afterward to prompt his activation the next morning. He takes the roster spot of starter Jeremy Bonderman, who went on the DL after a serious blot clot.
"We had a spot available, so it made sense," manager Jim Leyland said. "[General manager Dave Dombrowski] and I wanted to bring him back if he was OK, and he was OK."
The move gives the Tigers three left-handers in their bullpen, with Rapada joining Bobby Seay and Casey Fossum.
Reliever Aquilino Lopez will not return from the bereavement list Monday as planned, but not because Rapada took the open roster spot.
"There's been a setback there," Leyland said.
Rapada pitched two-thirds of an inning for Toledo against the Columbus Clippers. He took the loss after starting the eighth inning, allowing one earned run on no hits and two walks.
He struggled with his control early in the outing and found a rhythm against his last few hitters.
"At first I don't know what I was doing, but then I found my release point and I was able to throw all my pitches for strikes," Rapada said. "I'm pretty happy with it. As the inning progressed, everything got a lot smoother, I was getting more action on my ball. In the beginning, I was trying too hard, trying to do too much too soon. I had good sink on my fastball, my arm responded good and I'm ready to go."
The Tigers placed Rapada on the DL after he complained to the training staff of the ache in his arm in late May. The side-armer tried to pitch through the pain, but then thought better of it after a rough 18-pitch outing against the Mariners.
Rapada has recorded several big outs against left-handed hitters this season. In going 2-0 with a 4.50 ERA, he has allowed five runs on nine hits in 10 innings.
Scott McNeish is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.