It's been speculated that the injury originally occurred in a game against Baie-Comeau on November 19th, 2010; after which he missed 5 games before returning against Shawinigan in a 4-1 win on December 3rd, 2010. Leblanc played through the injury the rest of the season, winning a silver medal for Team Canada's under 20 World Junior Hockey Championship team and showing himself to be among their best players with 3 goals and 4 assists in 7 games, despite almost no powerplay time. He also managed a +6 on Team Canada. In the QMJHL Leblanc put up 26 goals and 32 assists in 51 regular season games, along with a +20 mark and 100 PIM. In the playoffs he scored 6 times in 10 games and added 3 assists and 16 PIM with a +4 rating.
Playing with a shoulder injury that requires surgery and possibly half a year of rehab and putting up those numbers is pretty impressive. It also might explain why his ice time was limited at the World Juniors, as he was clearly one of Canada's dominant players, but his shot didn't look exceptionally dangerous.
Even if Leblanc recovers quickly he's likely to miss Montreal's training camp in September and won't appear in the preseason like last year, and he will also likely miss the Hamilton Bulldog's training camp since he's of age to join the American Hockey League next season. It will be another test of Leblanc's perseverance to have to battle through this injury, possibly into November and have a successful rookie campaign in Hamilton.