The Rockies released Castillo on Saturday.
Castillo had spent most of the season on Triple-A Albuquerque's injured list while he recovered from a right lat injury suffered in spring training, but he was able to make it back from the shelf July 31 after a completing a month-long rehab assignment that included stops at two lower-level affiliates. He made just one appearance for Albuquerque, giving up four earned runs on three hits and three walks over 1.2 innings before the Rockies cut ties with him a week later.