Former Belgium international Radja Nainggolan has been arrested as part of an investigation into cocaine trafficking into Europe from South America, the Brussels public prosecutor's office said.
Brussels federal police carried out 30 searches on Monday morning, mainly in the province of Antwerp and in and around Brussels as part of the investigation.
The Brussels public prosecutor's office confirmed that the player was "deprived of his liberty in connection with this case."
The probe focuses on the alleged importation of cocaine from South America via the port of Antwerp, and its redistribution in Belgium, the office said.
After several months without a club, Nainggolan came out of retirement to play for second-tier Belgian side Lokeren-Temse. He celebrated his debut with a goal straight from a corner kick last weekend.
His new team said in a statement that they found out about his arrest from media reports.
"The club respects the presumption of innocence and therefore cannot comment further," it said. "We can only confirm that the player was absent from training this morning. The club will continue to focus on tomorrow's crucial league match against KAS Eupen. Radja Nainggolan is not eligible to play in that match anyway."
The 36-year-old Nainggolan has made 30 appearances for Belgium but has not played for his country since March 2018.
The central midfielder spent most of his career in Italy, notably playing for Roma and Inter Milan.
Nainggolan had several disciplinary issues throughout his career. When he played for Roma in 2018, he was fined and dropped from the squad for a match posting a video of himself appearing to be drunk and smoking during a party on Instagram on New Year's Eve.
When he played for Royal Antwerp in 2022, he was suspended after he was pictured smoking an electronic cigarette on the bench. The Belgian club at the time also mentioned how his behavior could negatively affect the squad.