The Blues placed Schwartz on injured reserve Saturday, one day after recalling forward Ty Rattie from Chicago of the AHL.
The injury is a huge blow to a team already missing top center Paul Stastny for four to six weeks with a broken foot and forward Patrik Berglund, who is out until January after undergoing shoulder surgery.
Schwartz, one of St. Louis' top forwards, was injured Friday in practice. He was helped off the ice and transported to a hospital, where he underwent the surgery.
The 23-year-old Schwartz has four assists in seven games this season. He scored 53 goals over the previous two seasons.