The Orioles recalled Zimmermann from Triple-A Norfolk ahead of the second game of Monday's doubleheader with the Blue Jays.
Zimmermann made 13 of his previous 14 appearances with the Orioles this season as a starter, but he'll be rejoining the big club as a long reliever. He'll step in as a multi-inning option in place of Beau Sulser, who was optioned to Triple-A following the Orioles' 7-3 loss in Game 1.