Nilis was one of the most prolific strikers in the 1990s, which provided particularly with its spectacular goals for attention. He began his professional career at Anderlecht, where he matured as world -class striker and Belgian national team. With the Belgian team, he participated in the 1994 World Cup in the USA, where he was eliminated in the second round against Germany. After the World Cup tournament, he moved to the Netherlands for PSV Eindhoven. After his first season in Eindhoven, he was elected Footballer of the Year in the Netherlands.
As an international, he played again for Belgium at the 1998 World Cup in France. Nilis remained despite numerous poaching attempts, particularly by British clubs until 2000 in Eindhoven. Only when 33 -year-old, he moved to the European Championship in 2000 in the Premier League for Aston Villa. He was injured on 9 September 2000 in a league match against Ipswich Town so heavy that he had to end his career in January 2001.
Successes with the team:
- Belgian Cup: 1987, 1991, 1993, 1994
- Belgian Cup: 1988, 1989, 1994
- Dutch Cup: 1997, 2000
- Dutch Super Cup: 1997
- Player of the year the Eredivisie: 1995
- Scorer in the Eredivisie: 1996, 1997