Manager Walt Weiss revealed that Castro is dealing with right shoulder inflammation, Thomas Harding of MLB.com reports.
Some people were wondering why Castro wasn't used in the ninth inning of Wednesday's game against the Reds when the game was tied, and it now appears to be injury-related. The Rockies are expected to make a decision on whether or not he'll require a disabled list stint or not within the coming days, so a timetable for his return should become clearer once the team makes that decision.