Corbin has not won a start since June 21, and in his nine starts since then, he has a 7.68 ERA. The D-backs lost eight of those games.
"He was disappointed," Arizona manager Chip Hale said when asked how Corbin took the news. "He understands that his pitching and his performance hasn't been good enough to stay in the rotation, quite frankly. He understood that this was a good way to work some things out, get in some non-pressurized innings and be able to do some things to work on stuff."
Corbin began the year as the team's No. 3 starter, and Hale said the team envisions him returning to the rotation -- if not this season, then in 2017.
"I understand," Corbin said of the decision. "It's been a frustrating year for myself. I know I'm better than what I've shown out there. I just need to continue to try to get better and go down there and do my job when my name is called."
In other D-backs news, reliever Andrew Chafin had his injury-rehabilitation stint cut short after he injured his groin. He had been rehabbing from left shoulder tendinitis.