"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's a winner. We want winners here, and he's a proven winner. He's won two Stanley Cups. He's 22 years old and been a big part of it. He's got all the right tools. He's got size (6-foot-1, 204 pounds) and strength. He's exactly what we were looking for. He's going to be a big piece of our team for many, many years to come.
— Blue Jackets GM Jarmo Kekalainen on Brandon Saad, who he acquired in a trade with the Blackhawks on Tuesday