Grossmann took part in the morning skate Sunday, but apparently sustained the injury at some point during the practice. Sunday will be the first game he misses this season.
Grossmann has one goal, three assists and a minus-1 rating in 30 games for the Flyers. The 28-year-old was acquired from the Dallas Stars last season.
Philadelphia has lost five of its past seven, falling into 13th place in the Eastern Conference standings. The Flyers already announced they'd be without forward Danny Briere for the game against the Penguins, who carry an 11-game winning streak into the contest.