Koch was sent down to Triple-A Reno following Wednesday's contest.
Koch was recalled to the big leagues just a few days ago and was able to make one appearance during his brief stay with the team, allowing three runs on two hits and a walk while failing to record an out during Tuesday's game. He was optioned in order to make room for Robbie Ray (concussion) on the active roster. The 26-year-old will continue to serve as organizational depth for Arizona, but he's unlikely to see any meaningful time on the mound with the club this season.