Koch was recalled from Triple-A Reno on Monday.
Koch will join the big-league bullpen in place of Braden Shipley, who was shipped back to the minors after tossing 5.2 innings of relief in Sunday's loss. He owns an unsightly 10.06 ERA and 19:13 K:BB through 34 innings with Reno this season, so he won't see any high-leverage innings with the Diamondbacks.