Aguero has missed the last five games after a recurrence of a hamstring problem last month, but after taking part in training this week, Pellegrini is ready to include the Argentine at Anfield.
The 60-year-old told reporters: "Sergio is OK. He worked all week with the squad normally. It's very important to have him back. He's a top player.
"It's very difficult for their defence to stop him and so it's very important for us."
City currently sit four points behind league leaders Liverpool with two games in hand.