The Diamondbacks optioned Koch to Triple-A Reno on Saturday, Steve Gilbert of MLB.com reports.
Koch was promoted from Reno on Tuesday to provide bullpen depth after Monday's 15-inning game and pitched two scoreless innings in Saturday's loss to the Cardinals before returning to the minors. The 27-year-old was optioned to make room on the 25-man roster for first baseman and outfielder Christian Walker.