"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.
He seemed to thrive on his own and didn't really need any push from me. I certainly don't want to get in the way of the coaches. You see how that goes sometimes. I never really worried about it and just enjoyed the ride.
— David Ekblad on his son's [Aaron Ekblad] journey to the NHL, signing with the Florida Panthers