Center is out indefinitely
Further tests were scheduled.
Horton, 18, was injured Sunday when he got tangled up with Vancouver Canucks defenseman Brent Sopel and slid headfirst into the end boards late in the first period. Horton tried to shield his face with his left arm as he hit the boards but jammed his shoulder.
Horton, the No. 3 pick in last year's NHL draft, has 16 points in 44 games this season.
He has scored 10 goals, including four in his last four games, to rank third on the Panthers and fifth among all NHL rookies this season.
The timing of the injury is particularly unfortunate because, according to ESPN.com contributor Rob Parent, Horton lately has been showing the form expected of him when he was picked so high.
Information from The Associated Press was used in this report.
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