Wainwright, 36, has been absent since mid-August due to a right elbow impingement. He last pitched on Aug. 17, when he gave up seven hits and five runs in three innings.
Wainwright owns a 12-5 record in 23 starts, but his ERA is just 5.12.
The Cardinals plan to use him out of the bullpen for the rest of this season.
Wainwright is under contract for one more year at $19.5 million.