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.
The groove of being behind a bench is going to be interesting at first, but thank God we have a few exhibition games to get rid of those cobwebs. Overall the excitement of it all and the freshness and coming back refreshed, all those things are going to be assets. If [the players] come ready to give their best effort in practice and games, good things are going to happen. I'm always looking for results. It's not always on the scoreboard. It's winning and building something.
— Bryan Trottier on making his return to coaching as an assistant with the Sabres