2011-12: John Nyberg skated for the Frolunda U18 and U16 teams in Sweden and played for Goteborg in the TV-Pucken tournament for high school players. He had no points and was minus-4 with no penalties in 12 games for the Frolunda U18 team. Nyberg scored 1 goal with 4 assists and was +11 with 6 penalty minutes in eight games for the Frolunda U16 squad. In eight games during the TV-Pucken tournament he was +4 and had 2 assists.
2012-13: Nyberg spent the season with the Frolunda U18 team. He scored 4 goals with 10 assists and was +16 with 36 penalty minutes in 40 regular season games as Frolunda finished third in the South Division. Nyberg was minus-1 with no points and 2 penalty minutes in three playoff games.
2013-14: Nyberg played 19 SuperElit league games with the Frolunda U20 team and was the top scorer amongst defensemen in the U18 Elit League South Division. He scored 1 goal with 3 assists and was +8 skating for the Frolunda U20 team. In 33 regular season games for the Frolunda U18 team Nyberg scored 11 goals with 27 assists and was +27 with 32 penalty minutes. Frolunda captured the U18 bronze medal and in five playoff games Nyberg was minus-3 with 2 goals and 12 penalty minutes. Not among the 140 international skaters in the Central Scouting final rankings he was selected by Dallas in the sixth round (165th overall) in the 2014 NHL Draft.