Well, I'm not even sure if we should sign a CB. Ivanovic could replace Terry and I also believe in Zouma. It's hard to tell if a CB would fit in or not. Cahill played for the worst team in the Premier League when we signed him. Bolton's defense was a mess, but he had the potential and was confident enough to perform very well against Barcelona and Bayern München. On the other hand, Khalid Boulahrouz was quite expensive but turned out to be an awful player, so it's really not easy to predict. I think N'Koulou, Laporte, Musacchio, Inigo Martinez, Manolas or De Vrij all have the potential to become a starter at Chelsea and they could be all available for a couple of millions. Varane has just extended his contract, I can't see Real Madrid letting him go.