He started his playing career as an amateur for his local team AA Rekem, before achieving success with Standard Liège and PSV. Nicknamed “The Lion (of Flanders)”, Gerets was regarded as one of the top right backs in Europe at his peak and is considered one of the greatest players in Belgian football history. He is famous for having captained PSV to their first and only European Cup win in 1988.
As a coach, Gerets is best known for his advocacy of systems thinking. He is one of six managers – along with José Mourinho, Carlo Ancelotti, Giovanni Trapattoni, Tomislav Ivić and Ernst Happel – to have won domestic league championships in at least four countries.
Gerets began his career playing for amateur side AA Rekem before joining then titleholders Standard de Liège. Making his debut 16 April 1972 coming on for Silvester Takač against FC Diest. In the 1972–73 season Standard reached the Cup final, manager Vlatko Marković let Gerets start despite not being an established first team member as Standard lost 2–1 to fierce rivals Anderlecht. The following season, Gerets replaced 29-year-old Jacques Beurlet and became the first choice right back for the Rouches. In 1975 Gerets made his debut for the national team.
He is the third-most capped player for the Belgium national team, with 86 appearances and two goals.
In the 1980s, a new generation of players emerged at Standard. Noted manager Ernst Happel was hired, and later the club brought Raymond Goethals back to Belgium. Players like Arie Haan, Guy Vandersmissen, Michel Preud’homme, Walter Meeuws, Jos Daerden and Simon Tahamata became key players, whilst Gerets was the captain of the team. In 1980, Standard finished runners-up in the league, before winning the 1981 National Cup with a 4–1 win over Lokeren SC. In 1982, Standard won the title by beating Waterschei SV Thor in the last match of the season. A few days later, they faced Barcelona in the European Cup Winners’ Cup final, which they lost 2–1. The influence of Gerets on Standard’s success was recognised when he was awarded the 1982 Belgian Golden Shoe. The following year he captained Standard to another league title, their ninth overall, which would prove to be their last until 2007–08.
In 1985, Gerets joined PSV playing together with Ruud Gullit, Frank Arnesen, Huub Stevens and Willy van de Kerkhof followed by Brazilian star Romário. In 1986, Gerets won the title with PSV, and after the departure of Gullit in 1987, Gerets became the new captain. Under Guus Hiddink PSV won the league and cup double three years in a row, Gerets scoring twice in the cup final against Roda JC. In 1988 PSV reached the UEFA European Cup final facing Benfica. After 120 minutes, it was still 0–0; PSV eventually won on penalties.
In 1990, Bobby Robson was appointed as Hiddink’s successor. Under Robson, Gerets won another two titles with PSV then he retired at the end of the 1991–1992 season at the age of 37.