fee ever paid for an Allsvenskan player. Before signing with Dortmund, Isak reportedly turned down a move to Real Madrid. Isak made his first appearance for the club in a 3–0 cup win over Sportfreunde Lotte on 14 March 2017. Isak won his first medal with the club when Dortmund won the 2016–17 DFB-Pokal, only appearing once in the tournament, and not being in the squad for the final. He scored his first competitive goal for Dortmund in a 2017–18 DFB-Pokal second round win against 1. FC Magdeburg on 24 October 2017, scoring the second goal in a 5–0 win. Loan to Willem II After making no appearances in the 2018–19 Bundesliga season for Borussia Dortmund, Isak was loaned to Dutch Eredivisie club Willem II. On 28 February 2019, he scored the equaliser and the winning penalty against AZ Alkmaar in the semi-finals of the KNVB Cup, helping Willem II reach the Dutch cup final for the first time since 2005. On 30 March 2019, he became the first player ever to score three penalties in an Eredivisie match, in a 3–2 win against Fortuna Sittard. On 14 April 2019, Isak became the first foreign-born player in the Eredivisie to score 12 goals in his first 12 league games. Real Sociedad 2019–20 season On 12 June 2019, Isak signed a five-year deal with Real Sociedad, worth £988,000 a year, or £19000 per week, joining the La Liga club on 1 July 2019, in which he scored his first goal in his first game. He strongly continued the pre-season, scoring four goals in five games. Isak scored his first competitive goal for Real Sociedad in a 3–1 La Liga win against RCD Espanyol on 22 September 2019. On 6 February, Isak scored two goals and made one assist in the Copa del Rey quarter-final against Real Madrid. On 9 February, he scored the winning goal in the Basque derby against Athletic Bilbao. On 3 April 2021, Isak won his first silverware with the club when he started and played in 89 minutes of the 2020 Copa del Rey Final in a 1–0 win against Athletic Bilbao, helping Real Sociedad win the 2019–20 Copa del Rey. 2020–21 season He scored his first hat-trick for the club on 21 February 2021 in a 4–0 league win against Deportivo Alavés, becoming the first Swedish player to score a La Liga hat-trick since Henry "Garvis"