2008-09: Johan Mattsson played in one game with Sodertalje’s U20 club registering a 3.00 GAA and a .927 save percentage.
2009-10: Mattsson appeared in 20 games for Sodertalje U20 and put up a 3.74 GAA and a .892 save percentage.
2010-11: Mattsson played the full season with Sodertalje’s U20 club, posting a .930 save percentage and a 2.62 GAA in 26 games for the club. He also played in two playoff games, with a 5.04 GAA and .836 save percentage.
2010-11: Mattsson played the full season with Sodertalje’s U20 club, posting a .930 save percentage and 2.62 GAA in 26 games for the club. He also played in two playoff games, with a 5.04 GAA and .836 save percentage. Ranked seventh amongst European goaltenders in Central Scouting's final rankings prior to the 2011 NHL Draft, he was selected by Chicago in the seventh round (211th overall) and drafted by Sudbury (OHL) with the 29th overall pick in the 2012 CHL Import Draft.
2011-12: Mattsson split the goaltending duties with Joel Vienneau for Sudbury in his first OHL season and was part of the gold medal-winning Sweden team at the 2012 U20 World Junior Championship. He appeared in 37 games with the Wolves and was 23-14 with three losses coming in overtime. He finished with a 3.16 goals against and .910 save percentage. Sudbury finished fourth in the Central Division and was swept by Brampton in the first round of the playoffs. Mattsson started three of four playoff games; posting a 4.82 goals against and .859 save percentage. He did not see any game action at the WJC as the third goalie behind fellow NHL prospects Johan Gustafsson (Minnesota) and Anton Forsberg (Columbus).
A big goalie who fills the net well and relies on positioning more than athleticism to get the job done. Needs to improve quickness and rebound control.
Mattsson joined the Tri-City Storm in the USHL for the 2012-13 season.