I'd rather have a defender who's good and experienced now than one who's inexperienced but can become something better later. The club is currently building up Criscito, so I don't see the sense in this.
Edit: And yes I know we are in dire need of defenders, but I don't think 10 million Euros is really a fair price for a prospect. There are more experienced defenders out there available for less or an equal amount of cash.