"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.
It was a big dream. [Messi] is probably the best athlete out there, so it's a big honor, for [Kuznetzov] as well. It's maybe a once in a lifetime opportunity to meet the best player in soccer right now. I'm a big Barcelona fan and Messi fan, so it's huge. You can take [Michael] Jordan, [Mark] Messier, [Wayne] Gretzky, those kinds of [people]. It's an honor to meet. It's nice to be in that position.
— Washington Capitals forward Alex Ovechkin told told Monumental Network after meeting soccer star Lionel Messi prior to Argentina's practice at Fed Ex Field in Landover, Md. on Friday