 Hagen has been a FIFA referee and refereed UEFA Europa League, UEFA Euro 2012 qualification, and World Cup qualifying matches since 2009.On 19 October 2011 he got his first match as a UEFA Champions League-referee when A.C. Milan met BATE Borisov at San Siro.He got his second Champions League match on 22 November 2011, when Basel won Oțelul Galați 3-2 in Bucharest.