To fill Oswalt's roster spot Monday, the team recalled outfielder Charlie Blackmon from Triple-A Colorado Springs.
Blackmon is in his second stint with the Rockies this year. He batted .240 (6 for 25) in 12 games earlier this season.
Oswalt is 0-4 with a 7.64 ERA in four starts with the Rockies since signing a $2.3 million, one-year contract on May 2.
The 35-year-old right-hander, a three-time All-Star with Houston and the 2005 NL Championship Series MVP, went 4-3 with a 5.80 ERA in 17 games for Texas last season, including nine starts.
He won 20 games for the Astros in 2004 and again in 2005.