The 21-year-old rookie forward missed the past 10 games after he was injured in the first period of a 3-1 loss to the Anaheim Ducks on Jan. 30. He is expected to need six months to recover.
Selected by Boston in the fifth round (No. 146) of the 2014 NHL Draft, Bjork had 12 points (four goals, eight assists) in 30 games this season.
The Bruins (37-13-8), who are in second place in the Atlantic Division, one point behind the first-place Tampa Bay Lightning with two games in hand, visit the Toronto Maple Leafs on Saturday (7 p.m. ET; SN, NESN, NHL.TV).
Boston traded forward Frank Vatrano to the Florida Panthers on Thursday for a third-round pick in the 2018 NHL Draft.
