Red Bull Salzburg After playing for the youth team of SC St. Valentin, Schlager joined the
FC Red Bull Salzburg Academy in 2011, where he played in all teams. In 2015, Schlager was transferred to FC Liefering, the feeder team of FC Red Bull Salzburg. During the
2017–18 season, Salzburg had their best ever European campaign. They finished top of their Europa League group, for a record fourth time, before beating
Real Sociedad and
Borussia Dortmund thus making their first ever appearance in the UEFA Europa League semi-final. On 3 May 2018, he played in the
Europa League semi-finals as
Marseille beat Salzburg 3–2 on aggregate to secure a place in the
final.
VfL Wolfsburg On the 26 June 2019, Schlager signed for
Bundesliga club
VfL Wolfsburg. During his time with Wolfsburg, Schlager made 81 appearances in all competitions, including 69 in the Bundesliga. Schlager helped Leipzig to win the
German Cup and
German Super Cup in 2023, starting the latter, coming on as substitute in the German Cup Final. In early May of 2024, Schlager was playing against Hoffenheim, when he was substituted off with an injury. Later tests confirmed that his ACL was torn, and underwent surgery, therefore missing the European Championship in the summer. ==International career==