2009-10: 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 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. The 18-year-old must add more strength to play along the boards at the more physical men's level and will need improvement on the defensive side of the puck.
Collberg is under contract for another year with Frölunda in the SEL and will most likely have the opportunity to help Team Sweden defend the Gold Medal at the 2013 World Junior Championship. It is very possible that the young sniper could be playing in North America as early as the 2013-14 season.