The Rockies placed Castano on the 15-day injured list Sunday due to a right pectoral strain.
Castano will be eligible to return from the shelf July 3, but given the nature of his injury, he may need more than the minimum amount of time on the IL to make a full recovery. The 26-year-old had been occupying a low-leverage role in the Colorado bullpen since being promoted from Triple-A Albuquerque on May 21, recording one win and no holds or saves while pitching to a 3.93 ERA and 1.36 WHIP across 18.1 innings in nine appearances.