Karim Benzema’s lawyers are to take legal action after a transcript purporting to be a conversation between the Real Madrid striker and a friend which forms part of the inquiry into an alleged sex-tape blackmail plot against his France team-mate Mathieu Valbuena, was leaked and published.

The striker’s lawyer Sylvain Cormier said the publication of the conversation contravened the confidentiality of an official judicial investigation. He said the publication of the transcript, which was first reported by Europe 1 radio and later by the sports newspaper L’Equipe, was “a scandalous method”.

He told the Associated Press: “We believe the files have been leaked to the press to influence Valbuena’s future testimony.” The lawyers are to take action for “violation of judicial confidentiality” aimed at finding and punishing those who made the leaks. Another lawyer for Benzema, Alain Jakubowicz, said they would stop at nothing to find the person who was making the leaks.

Benzema was last week placed under formal judicial investigation while authorities investigae the allegation of conspiracy to blackmail and participating in a criminal group. Cormier insisits that Benzema was “totally innocent” and “played no part in any blackmail or attempted blackmail”.

Valbuena, a France and Lyon midfielder, went to the police after being contacted by an unknown man claiming to be in possession of an incriminating sex tape apparently recorded on a mobile phone.

The police investigation led them to three men who have been placed under formal judicial investigation.

According to L’Equipe’s transcript of the leaked phone call, Benzema says that he felt Valbuena thought it was all a joke.

“I don’t think he’s taking us seriously,” Benzema said. When Valbuena had asked if his tattoos could be seen in the video, Benzema had told him: “You can see everything.”

He says he had told Valbuena: “Anyway, do what you want, if you don’t want to pay, it’s your life, but I warned you.”

His lawyer insisted that Benzema was not involved and that he had tried to dissuade Valbuena from negotiating with the suspects.

Both Benzema and Valbuena were omitted from France’s squad for the games against Germany on Friday and England next Tuesday.

Real Madrid have said they are standing by their striker.

“The Real Madrid president, Florentino Pérez, held a meeting with the player in which he gave him his full support and expressed his confidence that his actions were in good faith and that he is completely innocent,” the club said in a statement.