The Premier League champions are struggling to defend the title they won back in May and Kurt Zouma says they must improve if they are to have any chance of securing it this season.
Jose Mourinho's side, who have just four points from their opening four ties, fell to their second defeat of the new campaign on Saturday when they played Crystal Palace.
The south London club beat the Blues 2-1 at Stamford Bridge in Mourinho's 100th home league game. And following the defeat to Alan Pardew's men, Zouma told Chelsea TV: 'We have to improve everything. Mentally we have to improve. The season after we are champions, it's really difficult to prepare ourselves.
'To improve is more difficult, but we have to improve ourselves and keep going, keep working.'
The west London club should have had a penalty when Zouma's shirt was pulled by Connor Wickham, but the 20-year-old said of the incident: 'I think it was a penalty kick. The referee didn't whistle, but the game wasn't over with that.'
Chelsea travel to Merseyside next to play Everton at Goodison Park on the 12th of September.