"We will know more on this within a day or two as we await results of tests," Holmgren said in announcing the injury.
Hartnell saw 17:13 of ice time in the Flyers' 3-0 loss at the New Jersey Devils on Tuesday. He has one assist and 13 penalty minutes in three games this season.
The Flyers will be without Hartnell, Brayden Schenn and Zac Rinaldo for Thursday's home game against the New York Rangers. Schenn was suspended by the NHL for one game for a hit on New Jersey defenseman Anton Volchenkov in Tuesday's game, and Rinaldo is out with a lacerated right thigh.
I feel that responsibility, I've felt it for the last two years. We core guys get a lot of minutes, we get a lot of opportunity out there. Our teammates, the organization and fans look to us to be the guys to put the puck in the net and to create momentum out there.
— Jordan Eberle on taking his game and the Edmonton Oilers to the next level