"Sore today," Oswalt said.
There were no immediate plans to place Oswalt, who is 7-8 with a 4.56 ERA, on the disabled list, manager Cecil Cooper said. "We're going to wait and see, probably by Sunday we'll see how he feels," Cooper said.
Cooper had hoped to use Oswalt as the Astros' starter in the team's first game after the all-star break Friday against Chicago, but conceded that was now unlikely.
"I'm sure it will push him back," Cooper said. "We were anticipating Friday...That probably won't happen."
Oswalt said if he was used as Houston's fifth starter following the all-star break, he could rest 10 days and perhaps avoid a trip to the DL.
"After the break, I'll see how it feels," Oswalt said. "Throw a few bullpens -- see how it feels."