Hartnell, an All-Star last season, was injured by a shot taken by teammate Kimmo Timonen in Tuesday's game against New Jersey. Flyers general manager Paul Holmgren made the announcement before Thursday night's game against the New York Rangers.
Hartnell had one point in three games. He led the Flyers with 37 goals last season and had 67 points.
The Flyers are still without forward Danny Briere (broken left wrist). Holmgren says it's 50-50 Briere will be available for this weekend's games at Florida and Tampa Bay.
It's something that you don't really envision starting this way, but when you put the work in you don't feel like it's unwarranted. You definitely don't envision it unfolding this way, but you do think you can be successful at this level.
— Senators goalie Andrew Hammond, who defeated the Jets on Wednesday to improve to 6-0-1 since making his first NHL start on Feb. 18