The 25-year-old has been criticised for his perceived lack of effort at the Spanish outfit this season, but Perez insists that the Frenchman is not for sale.
"I have faith in all the players in our squad. Karim is a great player and we get offers for him all the time, every summer," Perez told Punto Pelota.
"All I can say is that the coach is the one who has the authority to do what he believes is right."
A number of Premier League clubs have been linked with his services.