French rugby chief Bernard Laporte was detained by police on Tuesday as part of an investigation into tax fraud, say financial prosecutors.
Hours after the verdict the French Rugby Federation president also stepped down as vice-chair of World Rugby.
France will host September’s World Cup.
Laporte was also banned from holding rugby positions for two years, but that is suspended pending an expected appeal.
Nearly 2,000 French rugby clubs are voting whether to accept the appointment of interim president Patrick Buisson – who was given the post by Laporte – with results expected on Thursday.
“He was summoned for questioning by tax authorities, he went there with a lawyer specialising in tax,” one of Laporte’s lawyers, Jean-Pierre Versini-Campinchi, told French news agency AFP.
“It is perfectly scandalous that the prosecutors have chosen the date of Patrick Buisson’s election for the questioning and that the disclosure of this questioning was made on the same day,” he added.
According to AFP, the court ruled that Laporte had showed favouritism in choosing France’s shirt sponsor.
In March 2017, Laporte awarded a 1.8m euro (£1.5m) shirt-sponsor contract to close friend Mohed Altrad, the billionaire owner of Top 14 champions Montpellier.
Altrad was given an 18-month suspended sentence and 50,000 euro (£42,800) fine. Both men deny any wrongdoing, and Altrad’s lawyer said he would study the decision before deciding whether to appeal against it.
In February 2017, Laporte signed a 180,000 euro (£154,000) deal with Altrad group for his image reproduction rights and prosecutors claim Laporte did not deliver the services paid for.
Altrad’s logo still features on France’s shirts, with Laporte, 58, negotiating a follow-up deal in 2018.
Laporte, who coached France to the 2003 and 2007 World Cup semi-finals, was also found guilty of intervening with disciplinary action against Altrad’s club Montpellier. He was convicted of helping to reduce a fine against the club from 70,000 euros (£60,000) to 20,000 euros (£17,000).
In November, financial prosecutors searched the headquarters of France’s 2023 Rugby World Cup organisers as part of a government inquiry into the management of the organising committee.