The Swedish defenseman took a big hit from Sabres forward Marcus Foligno early in the 6-5 overtime loss on Tuesday in Buffalo.
Maple Leafs coach Randy Carlyle said Wednesday the team expects a recovery period of four to six weeks. He'll likely miss out on playing for his country at the world hockey championship next month.
The 25-year-old had four goals, 15 assists and 20 penalty minutes in 76 games with Toronto this season. In 187 career games, all with the Leafs, he has 54 points and 44 penalty minutes.
Toronto has two games left after a second-half collapse. It hosts Tampa Bay on Thursday before wrapping up Saturday night in Montreal.