Manager Bob Melvin said Thursday that Castillo is currently shut down from throwing due to left shoulder discomfort, AJ Cassavell of MLB.com reports.
Castillo has made just two appearances in the Cactus League this spring, and the last one was March 3. Given that Opening Day is now only two weeks away, the 27-year-old reliever seems likely to begin the 2023 regular season on the injured list.