Sky Sports understands Mendy will snub a move to Sunderland in favour of a switch to Marseille, but a deal has still to be agreed with Le Havre.
Louvel is not willing to disclose how much Sunderland have offered for the left-back and is waiting to see what Marseille will come up with.
"We have an agreement with Sunderland, but not with Marseille," Louvel told L'Equipe. "There are no offers at the moment. Nothing has materialised.
"Marseille's offer should not be lower than that of Sunderland's.
"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."
The 19-year-old has reportedly visited Marseille's pre-season training camp to undergo a medical, but Louvel is not troubled by the issue.
He added: "It does not shock me that he goes to visit Marseille. That sounds very normal for him to make his choice.
"But he knows that, to seal a deal with a club, you have to have the green light from Le Havre. And I repeat that we do not negotiate below what Sunderland have offered."
Premier League new boys Cardiff City and Marseille's domestic rivals Lyon have also been linked with Mendy, who is due to be part of France's squad for the European Under 19 Championship in Lithuania later this month.