Pellegrini has already brought in Brazilian midfielder Fernando from Porto, French fullback Bacary Sagna from Arsenal and goalkeeper Willy Caballero from former club Malaga but isn't convinced his impressive pool is enough.
"I don't think the squad is complete yet but we have six weeks before the transfer window closes," the Chilean told reporters in Kansas ahead of their friendly 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's purchasing plans may have been changed after striker Alvaro Negredo suffered a broken foot in the friendly win over Scottish side Hearts on Friday.
Pellegrini, who won the Premier League title and the League Cup in his first season in England last year, said the powerful Spaniard had an operation on Tuesday.
"Alvaro had surgery today on his broken foot and he will probably be out for two or three months," the former Real Madrid manager said.
"It is a blow for us because Alvaro is a very important member of our squad so obviously we will miss him."
City will face AC Milan, Liverpool and Olympiakos Piraeus on the U.S. tour before returning for the English curtain raiser, the Community Shield, against FA Cup winners Arsenal on Aug. 10.