2008-09: Erik Gustafsson skated in 40 games for Northern Michigan as a sophomore. He scored 4 goals with a team-high 30 assists and was +21 with 10 PMs for the Huskies, who finished sixth in the CCHA.
2009-10: Registered 3 goals, 29 points, and 26 penalty minutes in 39 games. He also served as team captain for the Wildcats. Was named CCHA top offensive defenseman for a second year in a row. At the conclusion of his junior season, Gustafsson signed an entry-level deal with the Philadelphia Flyers. The defenseman was then assigned to the AHL where he posted 2 goals and 5 assists in 5 games for the Adirondack Phantoms.
2010-11: Gustafsson made his NHL debut with the Flyers in February, appeared in two games later in the season and was the second-leading scorer for Philadelphia's AHL affiliate Adirondack. Gustafsson skated over 16 minutes in his NHL debut and averaged just over 8 minutes in two other appearances. He finished -1 with 4 PMs for the Flyers. In 72 AHL games he scored 5 goals with a team-leading 44 assists and was -5 as the Phantoms failed to reach the playoffs.
2011-12: Gustafsson shuffled between the Flyers and their AHL affiliate Adirondack in his second pro season. He scored 1 goal with 4 assists and was plus-12 with 2 penalty minutes; averaging 16:47 minutes of ice time in 30 games for the Flyers. He played in seven playoff games; scoring a goal in the series-clinching Game 5 in the first round against Pittsburgh and finishing the playoffs plus-four with 1 assist and 2 penalty minutes. Gustaffson had an even plus/minus in 28 games for Adirondack and scored 1 goal with 16 assists and had 14 penalty minutes.