Campbell broke his right fibula and is out for the remainder of the playoffs, general manager Peter Chiarelli said in a statement.
Campbell, 29, suffered the injury when struck by an Evgeni Malkin shot while Boston was short handed in the second period Wednesday night against Pittsburgh in the Eastern Conference final.
The centre was unable to get off the ice, but maintained his defensive position. Campbell even broke up a Pittsburgh pass attempt before the puck was finally cleared by a teammate, at which point he slowly reached the Boston bench before being helped through the tunnel to the team's dressing room.
The London, Ont., native, in addition to killing penalties and being effective at the face-off circle, contributed three goals and four assists in 15 playoff games for the Bruins. He usually centres Boston's highly effective fourth line, with teammates Daniel Paille and Shawn Thornton.
Boston ultimately beat the Penguins 2-1 in double overtime in a game that stretched into early Thursday, to take a 3-0 lead in the series.
Game 4 is in Boston and will be shown on Hockey Night in Canada (CBC, CBCSports.ca, 7:30 p.m. ET).