Career
He spent the bulk of his career with Brøndby IF, but also played for the Greek club Panathinaikos and the Dutch club Football Club Twente. Brøndby
He played for Brøndby from July 1984 until July 1988, at the top level 1.Division in Denmark (later renamed Superliga in 1991). With a total appearance in 167 games during his first four years in the club, he was counted on as one of the most regular first team players at the pitch.
He scored several goals for Brøndby in 1984, but as he only played the last autumn half of the tournament, it was not enough to qualify him as the clubs topscorer of the year (that title went for Jens Kolding with 11 goals).
Claus Nielsen however subsequently managed to become the clubs topscorer for the next three years. By scoring 17 goals in 1985, then 16 goals in 1986, and finally 20 goals in 1987.
In 1985 Claus Nielsen was honored with the title "best Brøndby player of the year", and he also managed to qualify as the overall topscorer of the Danish league in 1986 and 1987. Panathinaikos
He played the 1988–1989 season for the Greek club Panathinaikos.
But with only 6 goals during 20 games, his time in Greece was only a limited success.
Football Club Twente
After his short Greek adventure, he played the next two seasons from 1989–1991 for Football Club Twente, in the Dutch Eredivisie. Here he continued to score a high rate of goals, by netting a total number of 22 goals in 39 games. Return to Brøndby
In July 1991 he transferred back to Brøndby again.
After playing 13 games in autumn 1991, he unfortunately started to suffer from a serious knee injury.
This injury kept him away from the pitch, throughout the entire spring 1992. He made a short comeback attempt in autumn 1992.
But unfortunately the knee injury continued to trouble him, so he only played 4 additional games for the club in the autumn (with the last one in November 1992). Because of his knee injury being more or less a permanent problem, he decided to end his football career in March 1993.
He played 14 games and scored 8 goals for the Denmark national football team from October 1986 to June 1991.
Unfortunately his knee injury put an early stop to his (at only 27 years of age).