Aguero is poised to return to action for City after eight games out with a calf injury.
The Argentina striker had been City's outstanding player this term, having scored 19 goals, before breaking down in the 6-3 defeat of Arsenal on December 14.
The 25-year-old has now recovered and could be involved as City host Blackburn in an FA Cup third-round replay at the Etihad Stadium tonight.
Pellegrini said: "You never know but I hope that he will come back the same way as before he was injured.
"He was in a good moment and maybe he needs two or three games to return to that level but Sergio will do it."
City have actually fared well without Aguero, winning seven of those eight games played in his absence and drawing the other - against Blackburn at Ewood Park.
The forward line has continued to fire with Alvaro Negredo taking his tally to 19 to equal Aguero and Edin Dzeko moving on to 13.
Pellegrini said: "Negredo is doing very well and we have Edin Dzeko as well who is a very important striker for us.
"When Sergio was injured Edin started to play often and he scores a lot of goals for us.
"But Sergio will always be an important player for us, not only because of his goals but he gives us a lot of play during the match."
Samir Nasri, Yaya Toure and David Silva will all be missing through injury and Pellegrini is likely to make other changes against Rovers.
But Pellegrini insists the competition remains high among the priorities for a team chasing glory on four fronts.
The Chilean said: "It's a very important cup because it's a very traditional cup, so the most important thing for this team is to have the mentality to try to win no matter what competition you are playing.
"I don't understand the reason why because we're not playing the Premier League that you don't want to win.
"If you make some rotations and the other team is strong they play better and win, then we would be eliminated. So, we will try to do well and try to continue."
Winning the quadruple would be a unique achievement but it is still an unlikely scenario and, although that might be a dream, Pellegrini is not thinking about it.
He said: "It's important to have the mentality at least to try.
"During the season with injuries and the amount games we have to play it's very difficult, and that's why no-one's done it before.
"But you must have the mentality to at least try to do it and that's what we're trying to do at this moment.
"We're not thinking about winning the four competitions, we're just thinking about Blackburn in the FA Cup and then to try and win against Cardiff on Saturday."