The D-backs right-hander will start on Sunday against the Brewers in place of Daniel Hudson, who suffered a torn ulnar collateral ligament in his elbow. D-backs manager Kirk Gibson said Collmenter will also start next Friday.
Collmenter began the year in the rotation, but after five starts and an 8.46 ERA he was sent to the bullpen.
In addition to Hudson, the D-backs are also without the services of Joe Saunders, who was placed on the disabled list Saturday with inflammation in his shoulder.
Collmenter has had good success in his short career against the Brewers. In three career regular-season games, including two starts, he is 1-0 with a 1.17 ERA against them. Last year in the National League Division Series he held Milwaukee to just one run over seven innings in a must-win Game 3.
"He's thrown great since we put him as the long guy, he has good experience in Milwaukee," Gibson said. "Then we can kind of reassess and see how quickly Joe is responding. He seems like he could be sooner than later."