Born in Tuusula, Koski started playing football in the youth teams of local clubs Tuusulan Palloseura (TuPS) and PK Keski-Uusimaa. He made his senior debut with PK Keski-Uusimaa first team on 13 May 2018 at the age of 16, playing in the 1–1 draw against JIPPO, in the third-tier league Kakkonen.[3]
FC Honka
In 2019, he joined the FC Honka organisation in Espoo. He played with the club's reserve team Honka II in Kakkonen for two seasons, before he made his debut in the premier division Veikkausliiga on 12 September 2020 with Honka first team, when he came in from the bench for the final minutes, in 1–3 away victory against Rovaniemen Palloseura (RoPS).[4] Despite his young age, in the next season Koski quickly established his place in the starting line-up and became an integral part of the team's defense.[5][6][7][8][9]
Koski scored his first goal in the league on 13 August 2022, in a 4–0 away win against Ilves.[10]
NK Istra 1961
In the early December 2023, it was announced that Koski had signed with Croatian premier division 1. HNL side Istra 1961 on a three-and-a-half-year deal.[11] He was already close to sign with the club in the 2023 summer transfer window but the deal got cancelled then.[12] The transfer was effective in January 2024.[13][14][15][16]
International career
A regular Finnish youth international, Koski has represented Finland at various youth national team levels. He has also captained the Finland U21 national team.[17]
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