"I cannot say at this stage how much he will cost but we are talking about one of the best young players in the world.
"But for us the most important thing is that the technical project is the right one for him. Franck is very young so we have to be very careful about his development.
"Chelsea are very interested and it is a great club but we must take our time to consider all the options.
"Now we are in January so he has to play at the African Nations Cup for Ivory Coast so I am not going to rush anything."