The Argentine star has plundered 26 goals himself this season despite being sidelined for the last month.
Pellegrini said: "Sergio is OK. He has worked the whole week with the squad normally and he doesn't have any problems.
"He is very important for us. We know Sergio is a top player, he is a player that it is very difficult for the other defences to stop, so he is very important for us.
"You always miss important players like Sergio Aguero."