Lille's vice general director Frederic Paquet has warned Chelsea not to approach star man Eden Hazard behind their backs.
The Blues have reportedly made an enquiry to the Ligue 1 club about the availability of the promising winger.
But Lille intend to keep hold of the 20-year-old Belgium international and have issued a hands-off warning to the West London giants.
Pacquet, speaking to French sports paper L'Equipe, said: "If Chelsea directly contacted Eden, we would take offence at it.
"That is not the right custom.
"No one is up for sale - that is very clear. We want to keep as many players as possible."