To fill Chen's spot on the active roster, the Royals have recalled right-hander Aaron Brooks from Triple-A Omaha. Lefty Danny Duffy will come out of the bullpen to take Chen's spot in the rotation. Duffy is slated to start Saturday against the Tigers.
Chen, 36, is 1-2 with a 7.45 ERA and 3.70 WHIP through four starts this season. Last year he was much more effective: 9-4 with a 3.27 ERA and 1.18 WHIP. As for Duffy he's been impressive in relief this season, and in 2013 he posted a 1.85 ERA in five big-league starts.