With under a minute to play in the opening frame, Halak sprawled to stop a shot from the point by Minnesota's Jared Spurgeon. The shot went wide and deflected off the end boards, but Halak laid face-first on the ice for several moments after play was stopped. He skated off the ice under his own power and went immediately to the locker room.
He was replaced in goal by Brian Elliott and did not return to the bench.
Blues coach Ken Hitchcock said following the game -- a 4-1 Blues victory -- that Halak will likely miss some time because of the ailment.
"Unfortunate injury, looks like its going to be awhile, so we'll have to wait and see and get a better evaluation of it tomorrow," Hitchcock said.
Hitchcock noted that goaltender Jake Allen, just returned to Peoria of the American Hockey League Saturday, will likely need to return to St. Louis to back up Elliott, who made 19 saves in the win Monday.
Halak missed several starts in early February with a sore groin, but it's unclear if Monday's injury is related.