Pellegrini, whose side host Sevilla in the UEFA Champions League on Wednesday, also said that Aguero's fellow injury victims Gael Clichy, Fabian Delph and David Silva could return to action next week.
In Aguero's absence, City thrashed Bournemouth 5-1 in the Premier League on Saturday, with Raheem Sterling claiming a hat-trick and Wilfried Bony scoring twice.
Pellegrini denies Toure talk
Pellegrini also played down an interview that midfielder Yaya Toure gave to French sports daily L'Equipe in which the Ivorian said he was "not happy" due to a perceived lack of recognition in the English media.
The Chilean declared: "He says he is not happy about [not being] recognised, [so people say] he is not happy here. But he is happy.
"It is different to not be happy about the criticism or the recognition, than to not be happy. They are different words. You can interpret how you want, but I think Yaya is happy here. He doesn't have any problems.
"I don't think I have to answer how important Yaya is. The answer is in his performances in the last four years. He always demonstrates it every game he plays."