Oswalt, who was attempting to tie the franchise record for career victories in the outing, was struck in the foot by a sharply-hit ground ball by Pedro Alvarez in the second inning.
Joe Niekro is the Astros' all-time wins leader with 144.
Houston manager Brad Mills said he expects Oswalt (6-11) to make his next start.
"He was really having some [dis]comfort in landing, and any time you have a situation like that with your pitcher the main concern is you don't want him to change something and put a stress on something else and start hurting something else," Mills said.
Oswalt, 143-80 in his career, pitched a one-hitter against Pittsburgh in his previous outing July 8. He earlier in the season requested a trade from the only team he has played for and has two scheduled starts remaining before the non-waiver trade deadline July 31.
Oswalt retired the first four batters he faced to extend his scoreless streak to 17 1/3 innings, but Alvarez's hit was the first of four consecutive. Oswalt retired only seven of his final 14 batters, allowing two runs and seven hits with five strikeouts.
"I was able to get through a couple more innings and I was hoping that I could get to the sixth, but it got to the point I started cutting my mechanics off and I didn't want to hurt myself trying to throw a different way," Oswalt said.
Information from The Associated Press was used in this report.