French Rugby Federation (FFR) President Bernard Laporte has claimed he is subject to a "coup attempt" after the official was one of five people questioned amid claims he favoured Top 14 club Montpellier.
Laporte is under investigation for his dealings with Montpellier owner Mohed Altrad, who is also being questioned by the French Financial Prosecution Office.
France 2023 World Cup chief Claude Atcher and FFR officials Serge Simon and Nicolas Hourquet are the other three officials who were taken into custody, according to L'Équipe.
Laporte, the World Rugby vice-chairman, faces investigation amid suspicions he pressured the French League's appeal committee into reducing a disciplinary sanction against Montpellier in 2017.
Montpellier is owned by billionaire Altrad, who heads the Altrad Group.
The club was punished for allowing fans to display banners criticising a proposed merger between rivals Racing 92 and Stade Français which was later aborted.
According to Agence France Presse, Laporte’s company BL Communication had signed an image-rights contract with the Altrad Group.
Laporte eventually pulled out of the deal.
Altrad currently sponsors the French national team and were backers of the country’s successful bid for the 2023 Rugby World Cup, which saw off competition from Ireland and South Africa.
The questioning of Laporte comes less than two weeks prior to the FFR Presidential election, where he faces a challenge from Florian Grill.
Laporte claimed in a statement that he is the victim of a "coordinated campaign" to destabilise French rugby.
"It is a real coup attempt, the motivation of the perpetrators of which is beyond doubt," Laporte wrote.
"All of this is part of a veritable, rather nauseating electoral strategy.
"As of this writing, I will be heard on Tuesday, September 22, in a preliminary investigation into what some have called the 'ALTRAD case.'
"This is a logical and normal step, resulting from a procedure that was started almost three years ago and for which I am eager to express myself.
"I want to tell you that this is a preliminary inquiry and as such there was objectively no urgency to hear from me before the election.
"Faced with the risk of interference with the electoral process and the fairness of the ballot, we requested a postponement of a few days from the PNF prosecutor in charge of this investigation.
"This has been refused to us on several occasions with the only explanation being that of scheduling difficulties.
"In this conjunction of calendars, I can only see it as a design.
"The press campaign around this convocation will be skillfully orchestrated to create a bad buzz in the media, it is written.
"This media tribunal has only one objective: to present myself in your eyes as guilty without the possibility of defending myself and by ignoring the presumption of innocence, a fundamental right protecting us all.
"I am very respectful of the work of the judicial system and I have been asking for months that this investigation be completed as quickly as possible."
Laporte claimed in his statement to French clubs that he knows "you are behind me" and said he would not allow "dirty tricks to steal your vote".
The FFR election is scheduled to take place on October 3.
The winner of the election would serve as FFR President when the country hosts the Rugby World Cup in 2023.
Laporte was Sir Bill Beaumont's running mate when the Englishman was re-elected World Rugby chairman earlier this year.
insidethegames has contacted World Rugby for comment.