City manager Manuel Pellegrini confirmed following his side's 3-1 win against Leicester City in the Capital One Cup that the striker will be out of action for around eight weeks, having limped out of their 6-3 win over Arsenal on Saturday after just 50 minutes.
Pellegrini revealed on Monday that his star striker would miss "at least one month", pending the verdict of club doctors, and the Chilean now believes that it could be as many as two months.
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"I don't how many weeks but it will be at least one month. It is very difficult to know at this moment how many weeks it can be."
Having missed Tuesday's game against the Foxes, Aguero could sit out as many as 12 matches should he be out of action for the full eight weeks.
If that is the case, he would surely be unable to make the first leg of the Barcelona clash, which is scheduled for February 18.
He will almost certainly play no part in Premier League clashes against Liverpool, Tottenham and Chelsea, as well as their FA Cup third-round tie with Blackburn.
City progressed to the semi-finals of the Capital One Cup after two goals from Edin Dzeko and one from Alexandar Kolarov helped see off Championship side Leicester at the King Power Stadium.