At Odense, he was a part of the team that won the 1993 Danish Cup and he was then brought to league rivals FC Copenhagen in 1994. He played a single season for the club, where he was team captain, before he moved to main rivals Brøndby IF in 1995. In his year at Brøndby, the club won the 1995–96 Danish Superliga championship, and Nielsen was named Brøndby IF 1995 Player of the Year.
At Odense, he was part of a team that won the 1993 Danish Cup and was subsequently transferred to league rivals FC Copenhagen in 1994. He played one season for the club, where he served as captain, before moving to main rivals Brøndby IF in 1995. During his time at Brøndby, the club won the 1995–96 Danish Superliga championship, and Nielsen was named Brøndby IF 1995 Player of the Year.