De Telegraaf newspaper reported that Nainggolan was arrested as a part of the investigation into drug trafficking in the port of Antwerp from South America to Europe.
In the news, more than 30 houses were made within the scope of the ongoing investigation.
36-year-old Nainggolan, who played in teams such as Cagliari, Rome and Inter in Italy, Antwerp in Belgium, was transferred to the third league team Lokeren-Temse at the beginning of the season.