According to the South Florida Sun Sentinel, the injury happened last week during an informal workout at the team's practice site, the Saveology.com Iceplex in Coral Springs, Fla.
Surgery was performed Sept. 6, but no recovery timetable was given by the Panthers except to say a full recovery was expected. The Sun Sentinel reported that the injury could sideline Gudbranson up to four months.
Gudbranson, 20, had two goals, six assists and a minus-19 rating in 72 games last season as a rookie. The third pick of the 2010 NHL Draft averaged 14:11 of ice time per game in the regular season, but that number rose to 17:06 per game in the Stanley Cup Playoffs. He was scoreless and a minus-2 in seven games in the first round loss to the New Jersey Devils.