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.
You don't see many. The [Drew] Doughtys, the [P.K.] Subbans, those are guys that create offense from the back and then on top of that ability, the size that he has. In the West you play against some pretty big players, and being able to clear the crease and contain the [Ryan] Getzlafs and the [Corey] Perrys and [Anze] Kopitars and players like that, we're excited about him going back there.
— Sharks general manager Doug Wilson on Brent Burns returning back to defense