Oswalt originally injured his hip in the sixth inning of his June 30 start against Los Angeles. He re-aggravated the injury in his next start 11 days later, leaving the game after throwing only 17 pitches against Washington.
The Astros will recall Runelvys Hernandez from Triple-A Round Rock to fill Oswalt's roster spot.
Oswalt is just 7-and-8 with a 4.56 ERA this season. Hernandez has gone 0-and-3 in three starts for the Astros this year.