Nilis was a beautiful football player with extraordinary kicking technique, especially when standing still. He could kick hard or with a curve. He relied on his technique and the inspiration of the moment. He made his Red Devils debut on 26 March 1988, but national team manager Guy Thys did not select him for the World Cup in Italy, which was the biggest disappointment of his career. He did play two World Cups (1994 and 1998) and played at the European Championships in 2000 for Robert Waseige.