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.
I definitely think going back down helped me, I had a lot of confidence down there, I played a lot of minutes and I think that helped me a lot. With the 37 games up here, that gave me experience as well. I know what it takes to play in the NHL and now it's time for me to show that I'm capable of being a full-time NHL player.
— Oilers forward Leon Draisaitl on finishing the 2014-15 season in juniors after playing 37 games with Edmonton to begin the season