The Manchester United goalkeeper will start his first derby on Sunday when the champions welcome local rivals City to Old Trafford.
Having spent well over £100million on new talent in the summer many expected Mark Hughes' men to be the club to break up the monopoly of the 'big four' this term.
However, after their 100 per cent record start to the campaign many have tipped the Blues to launch a serious title challenge but Foster believes City will need more time before they can be seriously considered a major player in the top flight.
"City will be up there but this season will be too soon for them," he told the News of the World.
"The 'big four' will probably be there come the end of the season. Hopefully United will be at the top.
"We are genuinely not thinking about City. It will take time for them to gel. When you get a lot of players come in it's hard to know what other players are doing."
Foster admits that he has noticed a change in atmosphere in training over the past week as derby day approaches and the England shot-stopper cannot wait.
"Everyone raises their game 10 or 20 per cent for these matches and the atmosphere will be electric."