"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.
When we started our journey we made a commitment to our fans to be relevant and to see the Chicago Blackhawks become the best professional hockey organization. There are not two finer symbols of that than Jonathan Toews and Patrick Kane. The commitment we have made to these incredible young men is equal to the commitment they have made to our team, our fans, our entire organization and the city of Chicago.
— Chicago Blackhawks owner Rocky Wirtz on signing Jonathan Toews and Patrick Kane to contract extensions