fourth consecutive DFB-Pokal final. On 20 May 2017, Papastathopoulos reached 100 appearances with Dortmund in Bundesliga in a home game against SV Werder Bremen and secured automatic qualification to the group stage of next season's UEFA Champions League. On 27 May 2017, in his fourth DFB-Pokal final in a row, Borussia Dortmund claimed a first DFB-Pokal win since 2012 as Pierre-Emerick Aubameyang's penalty defeated Eintracht Frankfurt 2–1. On 5 August 2017, as the captain of the club, he lost the 2017 DFL-Supercup on penalties' game against Bayern Munich. On 17 September 2017, he scored at the end of the first half against 1. FC Köln, giving a lead of two goals in his club. It was his first goal for the 2017–18 season and was secured with the use of VAR (Video Assistant Referee) method. On 14 October 2017, Borussia Dortmund's unbeaten start to the season was ended by RB Leipzig's 3–2 away win, as the Greek defender initially in trying to push the ball away helped Leipzig winger Yussuf Poulsen to score, while at the beginning of second half, was sent off for a foul in the box and Jean-Kévin Augustin scored the penalty. On 17 October 2017, after losing its UEFA Champions League opening games in Group H to Tottenham Hotspur and Real Madrid, Dortmund needed a win to kick-start its campaign in Europe's premier club competition, but they succeeded only to seal an away draw against Cypriot champions APOEL, as the Greek defender equalized with a header to Mario Götze's cross. On 4 November 2017, in the derby against rivals Bayern Munich he suffered a leg injury, during the first half, and was substituted by Jeremy Toljan, and two weeks later in an away game against VfB Stuttgart has received a heavy blow and replaced at the end of the first half from Dan-Axel Zagadou. Arsenal On 2 July 2018, Arsenal announced that Papastathopoulos had agreed a long-term contract with the club for a reported fee £17.6 million and would wear the number 5 shirt. On 12 August 2018, he made his official debut with the club as a starter at Emirates Stadium, in a 2–0 loss against champions Manchester City. On 4 October 2018, Papastathopoulos scored his first for the club, setting the Gunners on their way to a comfortable 3–0 victory over Qarabag in the 2018–19 UEFA Europa League group stage: after just four minutes