Zimmermann was recalled from Triple-A Norfolk on Saturday.
Zimmermann was sent down in mid-June after struggling over his first major-league starts of the year, posting a 5.94 ERA and 1.47 WHIP in 66.2 innings. He didn't fare much better in the minors, logging a 4.50 ERA and 1.28 WHIP in 18 innings over three appearances (two starts). The southpaw was scheduled to start for Norfolk on Saturday but will rejoin the Orioles' active roster, likely as a long reliever for now.