The injury that caused Castillo to leave Thursday's game may be tendon-related, Dennis Lin of The Athletic reports.
An earlier report suggested that Castillo may have exited due to a blister, but the presence of a splint on his left middle finger after the game implies that the injury may be more severe. Castillo suffered the injury while pitching in his first major-league game this season following a stint on the 60-day injured list due to a left forearm flexor strain.