A judicial investigation was opened on September 2 after Paul told authorities a group had requested money for protection services stretching back 13 years.
Le Monde reports Mathias has decided to turn himself in to the authorities, who are looking into allegations of extortion with a weapon, kidnapping or kidnapping in an organised gang and participating in a criminal association.
He was then placed in custody, along with three other suspects.
Paul told police he was confronted by an extortion gang, which included his brother Mathias, during a trip back to his home suburb of Lagny-sur-Marne in March.
The midfielder says the group, which included two masked men armed with assault rifles, forced him to accompany them to a flat where they demanded money for protecting him.
When the gang continued to ask for money, Paul filed a criminal complaint through his lawyers.
Source: Marca