On 7 February 2019, 17-year old Mattson signed a trainee-contract with Silkeborg, after good performances for the first team in training and in friendly games.
[3] Mattsson started on the bench, before replacing Ronnie Schwartz in the 89th minute.
[4] Mattsson made his debut in the highest football league in Denmark on 8 July 2020, the same day he signed his first 4,5-year professional contract with Silkeborg.
[5] Pelle's older brother, Magnus Mattsson, is also a footballer, playing for F.C.
Their father, Joakim Mattsson, who is from Sweden, is a football manager.