I can understand what
@JSMHE is saying, though. If you look at most teams, they normally have 3 good enough defenders who could step up to the first team at any time. In our case next season, it would be Smalling, Evans and Jones. Chelsea have Cahill, Terry and Ivonovic, in which the latter spends most of his time at right back. Fortunately for Chelsea, Terry and Cahill very rarely got injured last season, and were able to form a good partnership.
I think because of the injuries of our centre backs over the last couple of years, it has led most of our fans to think we need another defender, and rightly so, but what happens if Smalling, Jones and Evans have an injury free season next year? What happens to the player we brought in? Who gets dropped from the starting XI and bench, because normally there's only one centre back on the sub bench.
Ideally, if I had my way, I'd kill two birds with one stone and get in a very good defensive right back, who could also play centre back - similar to Ivanovic. In this way, if/when Rafael is injured, that player could come in, and if two of our centre backs are injured, he could come in at centre back.
For example:
Rafael and Smalling injured - New Signing (RB and CB) - Jones - Evans - Evra
Smalling and Evans injured - Rafael - New Signing (RB and CB) - Jones - Evra
By killing two birds with one stone, if we were to sign a player who could play two positions (CB and RB), you'd expect him to still get a sufficient amount of playing time.
Question is, who's out there that can play that role? We've already got someone in Jones who, in my opinion, is great at CB and RB, but i'm not sure he wants to play RB.
We need a Wes Brown or John O'shea.