The Premier League champions are 12 points behind league leaders Manchester United ahead of this afternoon's fixtures.
The 28-year-old told reporters: "We are a team [built] over the last four years; it's not really easy for a team to build up the mentality to try to keep winning every year, like top teams around Europe.
"Probably this year we needed to show we wanted to retain the title and it's been very difficult. So we know that we need to do something more, give something more, try to do better, to create that strong mentality that we need.
"We know we have great, fantastic players but probably we have to be stronger as a group to be one of the top teams in Europe."
City face Aston Villa on Monday.