Mathias Flaga Olesen (born 21 March 2001) is a professional footballer who plays for Austrian Football Bundesliga club Grazer AK on loan from German side Greuther Fürth. Born in Denmark, he represents the Luxembourg national team.
On 10 June 2025, Olesen signed a two-year contract with Greuther Fürth in 2. Bundesliga.
On 2 February 2026, Olesen moved on loan to Grazer AK in Austria, with an option to buy.
Olesen made his international debut for Luxembourg on 11 November 2021.
Born in Denmark, Olesen moved to Luxembourg in 2007 with his family, as his father got a job there in the investment industry. Olesen attended the European School of Luxembourg II (ESL2).
1.FC Koln