2009-10: Sebastian Collberg made his men's hockey debut as a 16-year-old, skating in four games for Mariestad BoIS in the Swedish Division I. He played most of the season for Mariestad's U18 and U20 teams and represented Vastergotland in Sweden's TV-Pucken national tournament. Collberg scored once in his stint with the Division I team. In 26 games at the U20 level, including two post-season contests, he was third on the team with 25 goals and had 14 assists. Collberg scored 12 goals with 15 assists in 15 games for Mariestad U18. In eight games for Vastergotland he scored 6 goals with 5 assists.
2010-11: Collberg moved up to Elitserien club Frolunda, seeing time briefly with the men's team. He spent the majority of the season with Frolunda U20; seeing action in 12 games for Frolunda U18. Collberg also represented Sweden at the U17 and U18 level in 11 international matches but did not compete at the world junior championships. Collberg played just under eight minutes total in five Elitserien games but made his mark with the U20 team. In 35 games he was the team's second-leading scorer with 21 goals and 23 assists and in seven playoff games scored 4 goals with 5 assists. In 12 games with Frolunda U 18 (including four playoff games) he scored 10 goals with 8 assists.
2011-12: Collberg saw limited ice time in 41 games with Frolunda in his first full Elitserien season. He skated in 21 games for Frolunda U20 and in five games for Frolunda U18. Colberg represented Sweden at the 2012 U18 and U20 World Junior Championships – winning a gold (U20) and silver (U18) medal. Averaging seven minutes of ice time, Collberg finished -8 with no points or penalties in his Elitserien games. Playing for Frolunda U20 he scored 9 goals with 8 assists and 18 penalty minutes. In four playoff games with Frolunda U18 he scored 3 goals with 3 assists and was named AllSvenskan (U18) Best Forward. One of the younger players in the U20 WJC, Collberg scored 4 goals with 3 assists in six games and was the team's second-leading scorer behind Anaheim prospect Max Friberg. At the U18 WJC he scored 4 goals with 5 assists in six games as Sweden reached the finals before falling to the USA. Collberg was ranked third amongst European Skaters in Central Scouting's final rankings prior to the 2012 NHL Draft. Collberg was chosen in the second round, 33rd overall, of the 2012 NHL Draft by the Montreal Canadiens.
2012-13: Collberg gained his first experience playing pro hockey in North America as a 19-year-old, joining Montreal's AHL affiliate in Hamilton for two games in April at the end of his season in Sweden's Elitserien. He split the season between Frolunda and Allsvenskan club Orebro and skated with Sweden's silver medal-winning squad at the 2013 World Junior Championship. Collberg had no points and was -2 with the Bulldogs, who missed the AHL playoffs. In 35 games for sixth-place Frolunda he scored 6 goals with 3 assists and had an even plus/minus with 6 penalty minutes; averaging ten minutes of ice time per game. He had 2 assists and was -1 in five playoff games. Collberg scored 6 goals with 2 assists in 15 Allsvenskan games for Orebro. He had 4 goals with 2 assists and was -2 with 4 penalty minutes at the WJC. Sweden lost to the USA, 3-1, in the gold medal game.
Collberg is a very skilled forward with excellent skating skills and speed while possessing excellent one-on-one moves. The Swedish sniper doesn't shy away from the dirty areas, knows how to find the soft spots to score goals and has an elite wrist shot which he can release in a hurry with great accuracy and velocity. He must add more strength and size to play along the boards and will need improvement on the defensive side of the puck. The talented winger projects as a top-six forward at the NHL level.
Collberg has signed a three year NHL entry-level contract and could possibly be playing in North America this coming season. He needs to show that he possesses the strength and size to play against the bigger players at the pro level. The second round pick could be returned to Frolunda for another year and can represent Team Sweden at the 2014 WJC tournament.
Collberg was dealt by the Montreal Canadiens to the New York Islanders for Thomas Vanek at the 2014 NHL Trade Deadline.