Grossman sustained the injury in the second period of a 10-3 loss in Game 4 on Wednesday and could be out indefinitely.
Grossman did not travel with the team to Pittsburgh. Erik Gustafsson will take Grossman's spot in the lineup.
The Flyers are already without Marc-Andre Bourdon, who went down with an upper body injury in Game 1.
The Penguins will be without defenseman Paul Martin, who will miss his second straight game with an undisclosed injury. Pittsburgh coach Dan Bylsma says Martin's ice time will be split between Simon Despres and Brian Strait.