Castro (shoulder) was moved to the 15-day DL on Friday, the Denver Post reports.
The team does not believe Castro's injury is serious, and with a backdated DL stint, the 21-year-old will be eligible to return as soon as May 3. Jon Gray, Friday's starter against the Dodgers, was activated in a corresponding move. Castro was looking good before being shelved, and there's been speculation he could close some games toward the end of the season.