Coach Dan Bylsma says Kobasew was hurt in the first period of Monday's 3-1 win over the Carolina Hurricanes. Kobasew, who signed with Pittsburgh as a free agent in the off-season, has two goals in 12 games for the Penguins.
Kobasew's injury came one game after the Penguins lost defenceman Rob Scuderi with an ankle injury that will require surgery.
The Penguins are already playing without forward James Neal (upper body), forward Beau Bennett (undisclosed injury) and goaltender Tomas Vokoun. Vokoun is out until at least January while he recovers from a blood clot.
Pittsburgh forward Brandon Sutter did not practice on Tuesday. His status for Wednesday's game against Boston is unclear.
It was definitely emotional. I really appreciated the fans. It was a cool feeling and it felt special and the ovation there at the start and then you kind of feel funny out there standing by yourself. Thinking back, I was saying just a bit ago, you think back just trying to make the NHL and then you kind of reflect on all the years being able to play for a great organization here in Calgary and all the fun I've had so far in my career. I feel very fortunate and blessed.
— Boston forward Jarome Iginla on his return to Calgary, where he played for 16 seasons