Diddens was a small left winger at Racing Mechelen, which was the best team in the city of the Dyle river up until 1930. Jan Diddens, nicknamed ‘den bekker’ was an unforgettable player of the club. He was frequently selected for the national team, where he was less successful than at his club. Diddens did play two of the three matches at the 1928 Olympic Games and two matches at the 1930 World Cup.