Triple European champions Toulon have angrily denied allegations of doping.
Marseille prosecutors are investigating several pharmacies in Toulon, in the Cote d'Azur, after notification from France's anti-doping authority.
Reports allege Toulon players had been supplied with anabolic steroids.
Club owner Mourad Boudjellal said: "No player is concerned in this affair, it is totally unfounded information. This is related to a social security fraud that concerns the pharmacist not RCT."
Marseille prosecutor Brice Robin was also reported as saying that the investigation surrounded medication sales by Toulon pharmacists and no doping allegations had yet been proven.
Toulon have won the European Cup for the last three years in succession with former World Cup winner Jonny Wilkinson, 36, playing a key role in two before retiring at the end of the 2013-14 season.
Wales full-back Leigh Halfpenny, ruled out of the World Cup through injury, is among the team's superstar ranks, with Ireland captain Paul O'Connell set to join from Munster after the tournament finishes on 31 October.
Former France coach Bernard Laporte has played his part in Toulon's rich success and remains head coach for another season before departing to chase the presidency of the French rugby union.
Boudjellal hinted at internal politics amid Laporte's future ambitions as playing a role in the investigations.
"I have a strong feeling there is a will against Toulon and a person who is running for president of the FFR," he said.