Petr Cech will miss Saturday's showdown with Man City but could be back before the Champions League return leg against Inter.
The Czech keeper left the field after sustaining a bizarre calf injury in Wednesday's 2-1 defeat at the San Siro, with Henrique Hilario taking over.
The 27-year-old collapsed in a heap after taking a cross unchallenged on the hour mark and seems unlikely to make the clash with Wayne Bridge's Manchester City side on Saturday - although the rumours that he suffered cruciate ligament damage to his knee have been scuppered.
Asked about the severity of the injury, Ancelotti said: "We don't know now. We have to wait some days. We have to do a check control on his calf. We will take a decision and we will know how long he has to stay out."