Clermont head coach Franck Azema has questioned whether Toulon are remaining within the Top 14 salary cap.
Azema's outburst comes after his side suffered a first ever loss to Toulon at home last weekend at the Stade Marcel Michelin.
Highlighting the depth of Toulon's squad, with Ma'a Nonu set to make his debut this week, Azema wondered if his own club need to be "smarter" with their recruitment to match the European champions' quality.
"It seems to me that there is a rule where the salary cap is €10 million. Is everyone respecting that? Who checks this?" Azema told Midi Olympique.
"On the surface everything seems normal. Yet when I look at the size of Toulon's squad and the players they have even yet to arrive, I have to smile.
"With their numbers, I don't know how they manage to stay within the limits. Or maybe it's up to us to be smarter in the future.
"We will think about it and see what we can do, because obviously Toulon are smarter than us. It will be necessary to find some solutions."
Despite last weekend's 35-9 loss, Clermont remain in first place in the Top 14 with only three losses from their first nine matches.
Castres announced the signing on Tuesday of Clermont lock Löic Jacquet for next season.