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.
The 29-year-old Juventus midfielder told the Paris prosecution office that he had been the target of extortion by childhood friends since March and had paid £85,000 (€100,000) to that group in the spring, judicial sources told Reuters this month.
Franceinfo radio claimed that the group, armed with MI6 assault rifles, demanded £11million (€13m) from the French midfielder for 'protection services' stretching back 13 years.
The World Cup winner claims the gang has been threatening him for four months. Acts of intimidation were carried out in Manchester in April, and later around the Italian city of Turin, where Pogba currently plays for Juventus.
The gang is also accused of taking Paul to flat in the Paris suburb of Lagny-sur-Marne, where he grew up, at the end of March. There, the gang members accused the 29-year-old of not helping them financially since he became a professional player.
The initial investigations had been entrusted to the OCLCO, a unit within the judicial police tasked with investigating organised crime.
The extraordinary saga began last month when Paul's eldest brother Mathias released a video on social media, vowing he would soon make a series of 'great revelations' about the World Cup winner.
He said during the video: 'The French, English, Italian and Spanish public, as well as my brother's fans — and even more so the French team and Juventus, my brother's teammates and his sponsors — deserve to know certain things.
'In order to make an informed decision if he deserves the admiration, respect and love of the public.
'Whether he deserves his place in the French team and the honour of playing in the World Cup. If he deserves to be a starter at Juventus.
'If he is a trustworthy person, that any player would want to have at his side.'
Soon after the post was made, the Juventus midfielder released a statement - signed by his lawyers, his mother Yeo Moriba and current agent Rafaela Pimenta - admitting that Mathias' videos were 'unfortunately no surprise'.
The statement read: 'They (the videos) are in addition to threats and extortion attempts by an organised gang against Paul Pogba.'
'The competent bodies in Italy and France were informed a month ago and there will be no further comments in relation to the ongoing investigation.'
There was a claim that Paul Pogba had used a witch doctor to cast a spell on 23-year-old Mbappe, something which the Juventus star denies, and said was made up to discredit him.
'All of Paul's statements, from the hearing at the start of August – before my videos – to the response from his lawyers and the responses, from his supporters, are only intended to drag my name through the mud,' Mathias Pogba said in his latest TikTok video.
'So I'm asking myself: why rush to affirm that what I had to say concerned just witchcraft?
'Because it would be difficult to talk about the so-called blackmail in this case? So wouldn't it be better to hammer home that the big brother is just a jealous, money-grabbing person, ready to do anything to discredit before he speaks? Isn't that what all false accounts in my name are all about? No, we don't accept conspiracies here!'
Paul Pogba will miss two months of playing time for Juventus after undergoing knee surgery, putting his World Cup hopes in jeopardy.
Mathias Pogba, 32, is also a football player, who had spells in British football at Wrexham, Crewe Alexandra, Crawley Town and Partick Thistle.