With top scorer Sergio Aguero already sidelined until the new year with a knee problem, Edin Dzeko and Stevan Jovetic both missed last weekend's 1-0 Premier League victory at Leicester City.
Pellegrini revealed on Friday that the pair have not recovered in time for this weekend's meeting with Palace, meaning youngster Jose Angel Pozo is in line for a second consecutive start.
"We are without Jovetic, Dzeko, Aguero. We must change the way we play, a different system," he said.
Pellegrini also confirmed that Vincent Kompany is not ready to return after suffering a recurrence of a hamstring injury at Leicester.
"Vincent is recovering from his injury but he is not fit," the Chilean said.
The City boss then took time to comment on the futures of Frank Lampard, James Milner and Joe Hart.
Lampard - who scored the winner at Leicester - is set to see his short-term deal expire in January.
Pellegrini has already stated his wish to keep hold of the former Chelsea man, who is due to begin a new chapter in his career at New York City when the MLS season gets under way in March.
"We'll see. It is not just our decision. Of course I want him to stay but I cannot say 100 per cent at this moment," Pellegrini said.
On Milner, Pellegrini expressed his desire for the midfielder to sign a new deal, while fresh terms for goalkeeper Hart are close to being agreed.
He added: "There are a lot of things to decide [with Milner]... Yes I think [he will stay].
"I hope it is all finished [with Hart]. Maybe in the next couple of days we will have news."
