The Argentine left the Etihad Stadium to join Juventus earlier his month, while the controversial Italian signed for AC Milan in January.
"I think it's very important to have a very regular squad," Pellegrini told City's official website.
"I said the other day, [we need] two players by each position. We need two or three players more but we are not in a hurry.
"We need strikers, attackers. Comparing this squad with this year, here is not Balotelli and Tevez. They are very important strikers and we need to replace them so we are trying to bring at least one."
City have already signed Jesus Navas and Fernandinho this summer.