Hornqvist is in concussion protocol and was transferred to long-term injured reserve Monday, Jameson Olive of the Panthers' official site reports.
There's currently no timetable for Hornqvist's return but he'll be out through the league's holiday break at the minimum. Due to the nature of head injuries, the team likely won't provide much more information on his timeline until there's a definitive update. The Panthers recalled multiple players, including forwards Chris Tierney and Zac Dalpe, over the last two days.