He played 17 matches and scored one goal for the Danish national team, and represented his country at the 1986 FIFA World Cup and 1988 European Championship.
Frimann started his career with Danish club Akademisk Boldklub (AB) under manager Christian Andersen.
Frimann immediately got a place in the Anderlecht starting line-up, and he made his debut for the Danish national team in October 1983.
He was bought by Brøndby IF, and loaned out to Aarhus GF (AGF) in the 1988 season, where he won the 1988 Danish Cup.
In August 1990, Frimann ended his playing career, at 28 years of age, due to continued injury problems.
Copenhagen in October 1998, eight months before his contract expiry in June 1999, Frimann initially refused to let Andersen go before time and suspended him.