Le Havre president Jean-Pierre Louvel has informed Marseille that they must match Sunderland's offer for Benjamin Mendy.
The Black Cats have already reached an agreement with the Sky Blues, although Louvel is unable to disclose the fee.
According to Sky Sports News, the teenager has his heart set on a move to the Stade Velodrome, but Louvel is unwilling to back down on price.
"We have an agreement with Sunderland, but not with Marseille," the 62-year-old told L'Equipe. "There are no offers at the moment. Nothing has materialised.
"Everything will depend on Marseille's proposal. I have nothing against OM and I have a very good relationship with [president] Vincent Labrune.
"About the price, I have a confidentiality agreement with the English club, so I cannot tell you anything. But what is certain is that Marseille's offer should not be below that of Sunderland."
Cardiff City and Lyon have also been linked with the 19-year-old defender.
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