Career
Before that he played for Danish Superliga side AGF Aarhus, Norwegian side Vålerenga and Danish champions. Thomassen came to FCK from Calcio where he played in five years. In his youth years he played in AGF. He signed for Vålerenga IF on July 1, 2007.
Since he signed with AGF in 2008, he has been dealing with many injuries, which meant that he missed some vital matches for his team