Louisville right-hander Donn Roach was designated for assignment to make room on the 60-day roster for Balester, who was 0-0 with a 2.45 ERA and seven saves in 29 games for the Bats.
Parra was sidelined with biceps tendinitis and a left shoulder injury. This is his third trip to the disabled list this season. He was out from April 29 to May 25 with a strained neck and from July 20 to Aug. 4 with a left elbow injury.
Roach was claimed off waivers from the Cubs on July 13 and went 2-4 with a 6.00 ERA in seven games, all starts, for Louisville.