The Argentine international scored twice in Sunday's 4-1 thrashing of neighbours Manchester United at the Etihad Stadium but picked up an injury during the game.
While Pellegrini expects the striker to be fit in time for Wednesday's Champions League game against Bayern Munich, he confirmed that his star will not be risked at Villa Park.
We will leave him for next Wednesday but he will be absolutely fine.
David Silva is also expected to miss out once again as he recovers from a thigh problem, with Pellegrini explaining that he has an outside chance of playing on Wednesday, adding only: We will see in the week.
The City boss also insists that his team will not be distracted by the upcoming clash against the European champions and will need to play well to beat Paul Lambert's side.