Molina, 32, underwent surgery in July after suffering a ligament tear in his right thumb while sliding into third base in a July 9 win over the Pittsburgh Pirates.
A six-time National League All Star, including this year, Molina was batting .287 with seven home runs and 30 RBI in 83 games before the injury.
Catcher Tony Cruz has been optioned to Double-A affiliate Springfield.
The Cardinals opened Friday at 71-61, with a half-game lead over the San Francisco Giants for the first Wild Card spot in the National League.
Cardinals activate C Yadier Molina off 15-day disabled list. Option C Tony Cruz to Springfield (AA). — St. Louis Cardinals (@Cardinals) August 29, 2014
- Chris Johnson