He does not need surgery, the Bruins said. He reportedly will not be able to play for Slovakia in the 2015 IIHF World Championship, which begins May 1.
Chara, 38, was injured after taking a shot off his ankle April 4 against the Toronto Maple Leafs but averaged more than 24 minutes of ice time in the Bruins' final three games of the regular season.
Boston lost all three and missed the Stanley Cup Playoffs for the first time since 2006-07.
Chara finished the season with eight goals and 20 points in 63 games. He missed 19 games because of a knee injury sustained in October.
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