Mathias Pogba has been charged and detained over an alleged plot to extort money from his brother and France international Paul Pogba.
Four other people have also been placed under formal investigation for extortion and criminal association, judicial sources told news agencies Reuters and Agence France-Presse.
Mathias Pogba's lawyer, Yassine Bouzrou, said his client is innocent. He told French broadcaster BFMTV: 'We are going to challenge this decision.'
Earlier this month the Paris prosecutor's office opened a judicial probe into allegations by Paul Pogba that he was the target of extortion attempts and threats from an organised gang.