The team says Ennis will miss several weeks in announcing the news Thursday.
Ennis was hurt in a 4-0 loss at Boston on Monday.
It's the latest setback for Ennis, who missed the last half of last season because of concussion-related issues.
And it's another blow for the banged-up Sabres, who are already missing several regulars.
Ennis has scored 20 or more goals in three of eight seasons with Buffalo. He has a goal and assist in 12 games this season.