The Blues have already brought in midfielder Fernando, defender Bacary Sagna and goalkeeper Willy Caballero since claiming their second title in three seasons.
Gareth Barry and Joleon Lescott left when their contracts expired, but Pellegrini says his squad could alter further before the current transfer window closes.
"I don't think the squad is complete yet but we have six weeks before the transfer window closes," the Chilean said as his side prepared for a pre-season match against Sporting Kansas City.
"Perhaps there is the option to bring one or more players in, or maybe one or two will leave our squad but there is time for us to consider what is best for our team."
Pellegrini will be without striker Alvaro Negredo for the first part of the season after it was confirmed that the Spanish player had undergone an operation on the metatarsal injury picked up against Hearts last week.
"Alvaro had surgery today on his broken foot and he will probably be out for two or three months," the City boss added.
"It is a blow for us because Alvaro is a very important member of our squad so obviously we will miss him."