Chara, considered one of the top free agent defensemen signed during the offseason, agreed to a US$37.5-million, five-year contract on the first the day of free agency - July 1.
His loss comes during the team's worst stretch of the season. Boston entered Saturday's game on a three-game losing streak, having been outscored 20-3 in that span. The Bruins were beaten 10-2 by Toronto on Thursday, the first time they allowed that many goals since November 1997.
Chara has seven goals and 17 assists 38 games.