If Vidic can maintain his fitness and Rio signs a new contract than Smalling and Jones won't get many appearances at CB. We'll have to get games at RB. Don't think it is an immediate necessity.
I would like us to sign a midfielder in the Javi Martinez mode, some one who can play in place of Carrick and can also cover defense if needed. I hate the yearly two games where Carrick plays at CB.
It would be interesting to see how Fergie manages the attacking 4 positions. At this time we have:
Rooney, Van Persie, Hernandez, Welbeck, Nani, Young, Valencia, Zaha, Kagawa and Giggs.
That's 10 players. May be 9, if we see Giggs as a cover for the midfield too. That's one player too many in my opinion.