Halak suffered the injury in the first period of Monday's victory over the Minnesota Wild. The seven-year veteran missed time earlier this season with a similar injury.
The Blues recalled rookie goalie Jake Allen from Peoria of the AHL on Tuesday to help replace Halak. Allen figures to serve as a backup behind Brian Elliott, who replaced Halak on Monday and made 19 saves in St. Louis' 4-1 victory over Minnesota.
Halak is 6-5-1 with a 2.14 goals-against average in 16 games this season.
St. Louis (18-14-2) enters Wednesday tied with the rival Nashville Predators (15-14-8) for eighth place in the Western Conference standings.