The president of Marseille football club and two former directors were taken in for questioning Tuesday as part of a probe into transfers including that of top striker Andre-Pierre Gignac, sources close to the investigation said.
Vincent Labrune was taken into custody in Marseille along with director-general of the club Philippe Perez and former president Pape Diouf.
Another former president, Jean-Claude Dassier, was being held in Paris.
The investigation is looking into "contentious" money transfers "made in recent years", sources close to the investigation said. A police source spoke of "fraud linked to several transfers".
The transfer of Gignac from Toulouse in 2010 is part of the probe, which is being overseen by France`s organised and financial crime squad.
Several current and former officials from Marseille have already been questioned in the affair, and investigators have raided the club`s offices and seized documents in recent months.
Sources close to the case said there was "enough material" to "scrutinise the past and present management of OM (Olympique Marseille)" and the allegedly illegal transfers.
Those in custody "will have to explain themselves from top to bottom", the source added.