• In 2010-11, Klefbom made his debut in the Swedish Elite League at 17 years of age, playing 23 games for the Elitserien champions Frajestad. He was teammates with fellow draft prospect Jonas Brodin (No. 3 ranked European).

• He captained Team Sweden to a silver medal at the 2011 Under-18 World Championships finishing with four points (1-3--4) and a plus-four rating in six games. He generated 24 shots on net to lead all defensemen on the team.