Castillo has allowed seven earned runs over 5.2 innings across four Cactus League appearances this spring.
Castillo started spring training in the mix for a spot in the rotation, but it doesn't look like he's earned such a role through his performance. He allowed two runs on a hit and a walk over one innings in Tuesday's game versus the Mariners. Castillo is just 23 years old, so it's completely reasonable to assume he could use a little more time at the Triple-A level before making the jump full-time to the majors.