City's leading scorer has missed their last five games because of a hamstring injury but he has been training for over a week and is ready for a match which could go a long way towards deciding the Premier League title.
Pellegrini is now hopeful the Argentina international, who has scored 26 goals this season - but none since January - will be able to have an impact at Anfield.
Pellegrini said: "Sergio is okay. He has worked the whole week with the squad as normal. He doesn't have any problems.
"It's very important - he's a top player, it's very difficult for defences to stop him. It's very important for us.
"You always miss important players like Sergio - we also had a lot of other players injured during the year. But we have a squad prepared. You do not just depend on one player."
Pellegrini confirmed that their other main injury doubt - Yaya Toure - would be fit, leaving Matija Nastasic as their only absentee.
The City boss says that while the Liverpool game is huge for both teams, the result will not decide the destination of the Premier League crown.
"It's a very big game - a very important game. We play against a team that is top of the table. We play in their stadium. Liverpool have had a wonderful season so it's a big game and a very difficult game," he said.
Asked if the Anfield clash was the biggest of his time at City, he said: "No - the biggest game is every week. It's not a game that will decide the title.
"It's a very important game but we can beat Liverpool and then lose to Sunderland or West Brom. If we think that this game is more important than next Wednesday (against Sunderland) then we are not going to win."
Liverpool against Manchester City kicks off a massive Super Sunday - coverage from Anfield begins at 12.30 on Sky Sports 1.