Vanek suffered a lower-body injury during the first period of Game 2 Saturday afternoon when he was checked into the end boards behind the Boston net by Bruins defenseman Johnny Boychuk.
Vanek did not return to the game, which the Bruins won 5-3 to even the series at one game apiece.
Vanek, a two-time 40-goal scorer, has been one of the hottest players in the League over the past week. He scored 4 goals against Ottawa in the next-to-last game of the regular season on April 10, then added the Sabres' only goal in New Jersey the following day.
Vanek also opened the scoring in Game 1 against the Bruins as the Sabres claimed a 2-1 win in the series opener.