The French international footballer Karim Benzema has been placed under formal judicial investigation in connection with an alleged attempt to blackmail a fellow footballer over a sex tape.

A statement from the Versailles prosecutor said the alleged crime of conspiracy to blackmail and participating in a criminal group for which he was being investigated could carry a prison sentence of at least five years.

Benzema's lawyer Sylvain Cormier, told reporters after a hearing that Benzema was innocent and took no part in any blackmail. "He played no part, I repeat no part, in any blackmail or attempted blackmail," Cormier said.

The prosecutor's move to place Benzema under formal investigation – which in the French justice system does not confirm wrongdoing but means investigators have serious grounds for pursuing the matter – exposes Benzema to a lengthy period of doubt before the European Championship finals that France hosts next year.

Investigators will now have to determine whether Benzema played a role in the alleged extortion attempt against the France and Lyon midfielder Mathieu Valbuena over a sex tape.

Judicial supervision

Benzema was also placed under judicial supervision, meaning he cannot meet with the victim or other people charged in the case.

The Real Madrid striker admitted involvement in the alleged extortion case, telling investigators he approached the fellow footballer about the tape on behalf of "a childhood friend" but claims he did not think he was harming the other player.

A source close to the investigation said that Benzema had admitted while he was in custody that he had spoken to the player who was the alleged target of the sex tape.

“Karim Benzema has admitted speaking to [him] at the request of a childhood friend, who was approached by three blackmailers who were in possession of the sex tape,” the source said.

“Benzema said he had agreed with his childhood friend on what he should say so that his team-mate would negotiate exclusively with him.”

The three alleged blackmailers, who are all in custody, had first contacted a friend of Benzema’s brother seeking to involve the player in their extortion attempt, a source said.

Detectives had detained Benzema for questioning a fortnight after the former France and Liverpool striker Djibril Cissé was interviewed and released as part of the same investigation.

Suspects

Benzema (27) was summoned to the police station at Versailles shortly before 9am on Wednesday morning and spent the night in custody.

The affair centres on the alleged attempted blackmail of an international midfielder with a sex tape apparently recorded on a mobile phone.

Three suspects said to be in the “entourage” of several footballers have been officially mis en examen – the French equivalent of being charged – since October.

The police investigation into the alleged blackmail attempt was opened at the end of July. Cissé was interviewed and immediately released from further inquiries.

Cissé protested his innocence on French television, saying he had nothing to do with the case. He later announced his retirement from the game.

Benzema was driven away from the police station in Versailles outside Paris yesterday in a police car with tinted windows. – (Guardian service)