The former France defender told French daily newspaper L'Equipe: "I am going to do everything to make sure he does not go to just any club.
"With him, things are clear. After the season he's had, if he has to go, it will be to a big club. That's why I am standing in the way of a departure to Sunderland.
"I am not going to change what I said to him at the start of the year. If an offer comes from a big club, I will not stand in the way. The door is half-open."