"It was just to see how he felt," Cooper said. "It was great to see it felt great. That brings a smile to my face. He didn't feel any pain, so that's a good thing. I think (the injury) is all behind him."
Oswalt, an All-Star the previous three seasons, is 7-8 with a 4.60 ERA this year. He left his previous start during the seventh inning June 30 in Los Angeles with pain in his left hip. The sciatic nerve had been inflamed, causing the pain in the hip.
The Astros also optioned pitcher Runelvys Hernandez to Triple-A Round Rock and recalled right-hander Chad Reineke.
Hernandez was pounded for 10 runs in four innings Monday's start against the Pirates. He was 0-3 with a 10.29 in three starts.
Reineke, who has yet to pitch in the majors, was 3-8 with a 6.06 ERA in 12 starts for Round Rock. Cooper said the team needed a pitcher capable of throwing multiple innings in case of an emergency Tuesday after the bullpen was overextended in a 17-inning loss in Atlanta Sunday.
Houston has 13 pitchers on its roster now, but Cooper said it's likely that number would drop to 12 before Wednesday's game.
Starting second baseman Kazuo Matsui is eligible to come off the 15-day disabled list. He has not played since June 22 due to a strained right hamstring.
Cooper said Matsui "probably" would be activated Wednesday.
