As the influential central defender prepares to undergo a scan on the groin, it was being reported that he is facing four weeks on the sidelines.
That means he will miss Premier League fixtures against Cardiff, Hull and Stoke, with a return no doubt pencilled in for the derby against David Moyes' Red Devils on September 22.
In the meantime Pellegrini could step up his search for a new defender before the transfer window closes as he is already without injured duo Matija Nastasic and Micah Richards, with Joleon Lescott and the unproven Dedryck Boyata his only fit centre-halves.