2009-10: Erik Gustafsson split his second season in the Djurgardens club between the U20 and U18 squads. In 24 SuperElit league games with Djurgardens U20, he had eight assists and was plus-four with 26 penalty minutes. Djurgardens finished fifth in the South Division. In 27 regular season games for Djurgardens U18 he scored 7 goals with 13 assists and was plus-32 with 54 penalty minutes. He played in 3 of 5 playoff games and was an even plus/minus with no points or penalties.
2010-11: Gustafsson skated for the Djurgardens U20 team and led all defenseman with 21 assists. Playing on a Djurgardens team that finished first in the regular season and featured Ottawa prospects Marcus Sorensen and Mika Zibanejad and Nashville's 2012 second round pick Pontus Aberg, Gustafsson played in 38 regular season games and scored two goals while finishing plus-27 with 104 penalty minutes. Djurgardens reached the playoff semifinals and in four playoff games Gustafsson was minus-one with 1 assist and 6 penalty minutes.
2011-12: Gustafsson made his pro hockey debut as a 19-year-old – skating for Djurgardens in the Swedish Elitserien. In 41 games he scored 3 goals with 4 assists and was minus-three with 16 penalty minutes; averaging just over 10 minutes of ice time per game. After finishing 11th in the 12-team Elitserien, Djurgardens was relegated to AllSvenskan after finishing third in the six-team Kval series. In ten Kval series games Gustafsson had 1 assist and was plus-one with 6 penalty minutes. In 21 games with Djurgardens' U20 team he scored 3 goals with 11 assists and was plus-three with 14 penalty minutes. Not ranked among the 120 European skaters in Central Scouting's final rankings, Gustafsson was selected by Edmonton in the fourth round (93rd overall) of the 2012 NHL Draft.
2012-13: Gustafsson skated in 49 games for Djurgardens in Sweden's AllSvenskan (second league) and was the leading scorer amongst defensemen for the club. He scored 7 goals with 16 assists and was +12 with 52 penalty minutes. Djurgardens was fifth in AllSvenskan and was 2-3-1 in six playoff games. Gustafsson scored 1 power play goal and was -3 with 30 penalty minutes in six playoff games. In April 2013 he signed a two-year contract to play for Frolunda in Sweden's top league, the re-christened SHL.
Gustafsson is a skilled defender with good offensive potential to his game. He can run the powerplay, has good vision, and possesses a hard accurate shot with a quick release. For his slight built, he plays with a physical edge and can log big minutes in a game due to his smooth skating skills. He needs to gain more strength and improve his defensive positioning to play at the NHL level.
Gustafsson has signed a two-year contract with Frolunda of the Swedish Hockey League, beginning in 2013-14.