Career
Thomsen started playing football at Fjordager IF, before moving to Football Club Fyn where he already at the age of 16, was playing at the under-19 team Thomsen played several matches for the youth national teams of Denmark at a young age, and was in April 2010 (at the age of 15) tested by Blackburn Rovers together with 2 other youth players from Football Club Fyn. Thomsen came to OB at the age of 16 from Football Club Fyn, and started playing on the under-19 team
OB
At the age of 19, Greve was moved to the first team squad in March 2014 and did also sign a full time contract senior contract with OB. Thomsen got his debut for OB on 18 May 2014.
Thomsen started on the bench, but replaced Martin Spelmann in the 92nd minut in a 2-3 defeat against Football Club Copenhagen in the Danish Superliga. Thomsen signed a new one-year contract with OB on 6 June 2015.