Collmenter, who was the team's Opening Day starter, has been struggling of late. Entering Saturday, he had not won a game since May 6 and had a 7.76 ERA over that span.
"I'm smart enough to know that something could have happened," Collmenter said. "Obviously I wasn't pitching the way I need to be to stay in the place that I want to be. Hopefully it's a chance to get some innings and get some things ironed out and get my command back, and that's really been the biggest component of my lack of success."
In order to make room for Webster, the D-backs designated J.