Matthew Sean O'Riley is a professional footballer who plays as an attacking midfielder for Ligue 1 club Marseille, on loan from Brighton & Hove Albion. Born in England, he plays for the Denmark national team. O'Riley was an England youth international. As well as England, he is eligible to represent Denmark and Norway due to his mother's side of the family. In February 2022, O'Riley declared his interest in representing Denmark internationally when he stated that: "I played for England youth teams but at the same time, I do feel quite Danish. My mum is Danish and I can speak a decent amount and I can understand a very good amount. In that sense, I don't think it is out of the question at all. If I did get a call up from Denmark, I don't think I'd be saying no". In March 2022, O'Riley was called up to the Denmark under-21s for the first time. On 14 June 2022, O'Riley scored his first goal for Denmark against the Turkey under-21s in a UEFA European Under-21 Championship qualifying match - which Denmark won 3-2. On November 20 2023, O'Riley received his first senior cap for Denmark, starting in a UEFA Euro 2024 qualifying match versus Northern Ireland.