The Cardinals expect Molina back in action "within a three-week range," manager Mike Shildt said Thursday.
His move to the IL was retroactive to Monday. The nine-time All-Star, who missed 12 games in May and June with a similar injury, pinch hit on Saturday but hasn't started a game since July 3.
St. Louis will recall catcher Andrew Knizner from Triple-A Memphis before Friday's game against Arizona to fill in for Molina. Knizner made his big league debut June 2, going 0-for-7 for St. Louis.
The Cardinals also brought up left-hander Chasen Shreve from Memphis, optioned left-hander Tyler Webb and outfielder Rangel Ravelo to Memphis, and transferred pitcher Jordan Hicks to the 60-day IL ahead of their series against Arizona beginning Friday night.
Carpenter has been sidelined since June 29 with a lower back strain.
Shreve appeared in 20 games for the Cardinals last season, and is 2-1 with a 3.80 ERA in 37 games for Memphis this season.
Information from The Associated Press was used in this report.