Bruins General Manager Peter Chiarelli confirmed Kelly's right fibula was broken on a play during Saturday's 3-2 home victory over the Penguins in which Pittsburgh's Pascal Dupuis delivered a two-handed slash to the Boston player while along the boards.
Canada's TSN and the Boston Globe had reported earlier Kelly sustained a broken ankle.
Kelly has posted three goals and seven points in 28 games for the Bruins this season. It was his his second recent leg injury -- in March broke his left tibia, keeping him out of the Bruins' lineup until late in the post-season.
Orpik later on was carried off the ice on a stretcher after being punched in the face by the Bruins' Shawn Thornton, who now the subject of an NHL disciplinary hearing.
Duggar sisters unveil Christian dating rules in new book
Beautician charged with giving client fatal silicone butt injection