Castro (shoulder) struck out a batter and served up a home run in an inning of work with Triple-A Albuquerque on Monday.
Castro's shoulder is feeling much better, but the Rockies want to build up his strength more in the minors, so he'll stay on his rehab assignment for a little longer. An exact timetable for his return is currently unavailable, but it should become clearer once he appears in a couple more games with the Isotopes.