Career
He spent 11 seasons in the Bundesliga with VfB Stuttgart and Borussia Mönchengladbach. He played in two World Cup Qualifying matches in 1966. During his youth in Kiel, Sieloff aimed to become a boxer, having stood in the ring 25 times by the age of 14.
When his family moved to Rottweil near Stuttgart and after visiting football games of VfB Stuttgart at Neckarstadion, Sieloff"s interest however shifted from boxing to football.
In October 1960, he played his first game for VfB Stuttgart in the Oberliga Südaughter There he soon became a fixture in the stopper position in Stuttgart"s team
Physically strong yet technically adept, Sieloff soon got the attention of German national team coach Sepp Herberger, who first called him up for a 1964 friendly against Finland in Helsinki. During the next year, Sieloff became the standard sweeper of Germany.
As a player, Sieloff became known for surging forward from the sweeper position, often scoring with long range shots.
During the next four years, the sweeper position was usually that of either Willi Schulz or Karl-Heinz Schnellinger and thus Sieloff did not gain anymore caps up to 1970. After the 1970 Fédération internationale de football association World Cup, with Willi Schulz retiring from international play and Karl-Heinz Schnellinger not featuring regularly in the German lineups due to playing abroad, Sieloff revived his international career, which was also fostered by his success at club level with Borussia Mönchengladbach. In 1969, Sieloff had made the change from VfB Stuttgart to Borussia Mönchengladbach.
Foreign the 1969-1970 season, Mönchengladbach added Sieloff as sweeper as well as Ludwig Müller as the stopper.
With Sieloff being one of the celebrated stars of the team, he made his comeback for Germany in April 1970 in a friendly against Romania. After the 1970 World Cup, with Schulz retired, Sieloff once again became the starting sweeper of Germany.
However during 1971 it became apparent that Franz Beckenbauer, who previously played in midfield, was the strongest option at the sweeper position, which meant the end of Sieloff"s international career. Foreign Borussia Mönchengladbach, Sieloff played until 1974 when he moved to Alemannia Aachen, where he remained until 1976.
He ended his career in 1977, playing one season for TSG Backnang.
After his career, Sieloff became chief of the Mercedes Benz company-facilitated sports activities group. He died in December 2011. 1966 Fédération internationale de football association World Cup runner-up.