White Sox manager Will Venable said Thursday that Castillo has been moved to the bullpen, Jesse Rogers of ESPN.com reports.
Since being acquired from the Mariners on Aug. 2, Castillo hasn't provided the boost to the rotation that the White Sox had anticipated. Over his seven appearances (six starts) with Chicago, Castillo has labored to a 1-2 record, 7.76 ERA and 1.79 WHIP. In light of his struggles, the veteran right-hander looks like he could be limited to a low-leverage role out of the bullpen the rest of the way. Castillo had been lined up to start Friday versus the Tigers, but rookie David Sandlin is now on track to take over Castillo's spot in the rotation.