The Belgian midfielder joined the French club from Union Saint-Gilloise last summer in a deal worth €6 million and initially impressed under then-manager Franck Haise.
Vanhoutte had hoped his performances would strengthen his chances of earning a place in Belgium’s FIFA World Cup squad under Rudi Garcia.
However, as Nice’s form declined, his influence also faded and he gradually lost his status as a key player.
Despite the recent appointment of Olivier Pantaloni as the club’s new head coach, Vanhoutte’s future lay elsewhere, with his departure now officially confirmed.
Nice are understood to have avoided making a financial loss on the 27-year-old, who now begins a fresh chapter with Feyenoord.
