Career
He played 20 matches for the Danish national team, and represented Denmark at the 1992 Summer Olympics and 1996 European Championship. Born in Aarhus, Thomsen started his career at local top-flight club AGF Aarhus, where he initially played as a midfielder. Thomsen made his debut for the Danish under-21 national team in May 1989, where under-21 national team coach Richard Møller Nielsen used the 6" 3" Thomsen as a central defender.
Thomsen was named under-21 national team captain in 1990.
In December 1990, Thomsen signed a new contract with AGF, rejecting interest from Brøndby IF and B1903. In November 1991, Thomsen was scouted by Celtic Football Club manager Liam Brady, but the deal fell through due to "too many intermediaries" according to Claus Thomsen himself.
He also captained Denmark at the 1992 Summer Olympics, where he played all three of Denmark"s matches, and scored a goal against Mexico. In the fall of 1992, he lost his place in the central defence in AGF"s starting line-up, and he was used in a number of different positions.
He went on trial at Werder Bremen in December 1992, but was not signed by Werder manager Otto Rehhagel.
In June 1994, he moved abroad to play for English club Ipswich Town, in a transfer deal worth £250,000. He was called up for his Danish national team debut, by national coach Richard Møller Nielsen, in April 1995. Thomsen was called up to the Danish national squad for the 1996 European Championship, and played in all Denmark"s three matches before elimination.
He made a total 97 appearances and scored 8 goals for Ipswich.
He was one of the stronger players in the weakest side in Ipswich Towns history. In his first season he was relegated with Ipswich in 1994/5 and a major part of the side that missed the First Division Play Offs in 1995-1996 however as Ipswich were looking to improve their side in 1997 he was sold to Premiership Everton, for £900,000, in January 1997.
He did manage to score once at the right end for Everton, with a goal in a 2–1 defeat to Derby County. After little more than a year at Everton where his ineffectiveness has often since seen him included in Everton all-time worst XI team, he moved back to Denmark for £500,000 in March 1998, to play for Akademisk Boldklub (Bachelor of Arts).
He only stayed at Bachelor of Arts for six months, before moving abroad once again.
He joined German club VFL Wolfsburg in September 1998. In April 1999, Thomsen ended his Danish national team career, citing a lacking energy surplus. Due to injury problems, he saw very little playing time in his last years at Wolfsburg, and ended his career in April 2002.