The issues for Manchester City at center-back were highlighted over the two legs of their Champions League exit to Barcelona.
Martín Demichelis was given a red card for his foul on Lionel Messi in the first-leg and was suspended for the second-leg.
Joleon Lescott, Demichelis' replacement, was beaten by Messi for the first goal from Barça.
City were believed to be close to bringing in Porto's Eliaquim Mangala in January and is expected to arrive this summer to help Vincent Kompany with duties on defense.
