Belgian police raided the offices of Anderlecht and the national football association on Wednesday in relation to a money laundering investigation involving agents and player transfers.
A spokeswoman for the Brussels club told public broadcaster VRT that Anderlecht was cooperating fully with the probe and a spokesman for the Belgian FA told Reuters that police had taken away documents relating to transfers from its headquarters.
A spokesman for the federal prosecutor said: "We had some questions for the agents who took care of the transfers. It is a question of money laundering."
VRT and other local media said prosecutors were looking into transfers made before a 2017 change of ownership at Anderlecht and had also raided an agent's office in the capital.
Among the transfers being probed, the media said, was the sale of Serbia striker Aleksandar Mitrovic to Newcastle United in 2015. The Premier League side did not immediately respond to a request for comment.
The prosecutor's spokesman declined to give details of the three raids in Brussels on Wednesday. He said that they were not linked to the wide-ranging "Footballgate" probe into match-fixing and fraud which rocked the domestic league last year after the national side's third place finish at the World Cup.
The raids come at a miserable time for Anderlecht, champions in 2017 and historically Belgium's most successful club.
Dismal form has prompted a fan revolt that saw them fined and docked points this month when crowd trouble forced a match at arch-rivals Standard Liege to be abandoned; they then fired coach Fred Rutten after just 13 games in charge.
Now, the two-times holders of the Cup Winners' Cup and 1983 UEFA Cup winners are on the verge of failing to qualify for European competition next season for the first time in 55 years.
