Blues coach Ken Hitchcock disclosed his decision Monday.
Halak was injured in the second game of the Blues' first-round series against San Jose, leaving with an undisclosed lower-body injury that is believed to be a sprained left ankle he suffered during a collision with teammate Barret Jackman.
St. Louis had the deepest goalie tandem in the NHL this season. Brian Elliott led the NHL with a 1.56 goals-against average, including nine shutouts.
The NHL has not yet announced specific dates for the Blues-Kings series.