Zimmermann (hamstring) allowed a run on two hits and two walks while striking out four over three innings for Triple-A Norfolk in its game versus Durham on Wednesday.
Zimmermann missed nearly two months with the injury. The 29-year-old southpaw has pitched exclusively in the minors this year, though he could be an option for the Orioles in the second half, as the major-league club is in need of pitching help. Zimmermann has a 4.25 ERA, 1.47 WHIP and 38:15 K:BB over 42.1 innings with Norfolk and could be a spot starter or long reliever if he gets back to the majors this season.