The Anfield boss said: "Will their money make it more difficult for us? At this moment you never know.
"All we are thinking about is this game now and in January we will see what will happen. But it's not easy to improve a squad. Chelsea were spending money for years before they could win the title.
"In the future you never know how dangerous City's potential will be. Every year you hear about the possible challenges from Aston Villa, Newcastle, West Ham. Now it is City."
Benitez also insists City will not be the only team looking to spend.
He added: "You also have to take into consideration the level of the other teams.
"Money can help to sign the best players. But you must realise how hard the Premier League is to win."