Aguero injured a hamstring playing for Argentina shortly after scoring five goals for City in the 6-1 victory against Newcastle United last month.
"Sergio is fit and ready to come back, David (Silva) continues to have some small pain in his ankle so it’s a risk for him to play," Pellegrini told a news conference.
"Unfortunately Samir Nasri, Wilfried Bony and Vincent Kompany are also injured."
Aguero, last season's top Premier League goalscorer, has missed the club's last seven matches in all competitions, but they have remained unbeaten in that time.
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"We are doing a good season," Pellegrini said.
"We are the only English team (already) qualified for the next stage of the Champions League and are top of the table.
"It's important to try and continue in the same way."
Saturday will be a big day for 20-year-old England international Raheem Sterling, due to play against Liverpool for the first time since leaving them in the close-season for a fee that could rise to almost 50 million pounds ($76.25 million).
England team mate James Milner, who moved in the opposite direction, is expected to be in the Liverpool team.
"It’s always special, not only for Raheem, to play against a team (where) they spent a lot of years, for James Milner the same, that is part of the career of the player and they are now defending another shirt," Pellegrini said.
"He is a very young player and he must improve a lot... I’m happy with how he’s playing so far, he’s an important player and will be a more important player in the future.
"It depends on the way he improves... he has years to improve and I think he will be an important player not just for Manchester City but for England."
(Reporting by Steve Tongue; editing by Toby Davis)
