Chelsea boss Maurizio Sarri feels his side must tighten up at the back if they are to maintain their Premier League momentum and launch a title challenge this season.
Eden Hazard's hat-trick saw the Blues come from behind to beat Cardiff City 4-1 at Stamford Bridge on Saturday, extending their 100 per cent record under the Italian.
But Sol Bamba's surprise opener for the visitors demonstrated Chelsea’s vulnerability at the back, with Cardiff boss Neil Warnock warning his opponents they will need to be better against elite teams.
Sarri agreed with Warnock's assessment, with his side having only kept two clean sheets in their five Premier League victories this term.
"I think he's right. We are very dangerous in the offensive phase, but in the defensive phase we need to improve," Sarri said.
"We need to improve very quickly, but I think we can do it. Eight players arrived for training at the beginning of August, so I think it's normal that in this period we have some defensive problems.
"We can cover our problems with quality in the offensive phase, but not in the defensive phase. I have to organise better the defensive phase and the players have to understand that.
"My opinion in this moment is two teams, Liverpool and Manchester City, are better than the others. We have to improve step by step but as I said before, my target is to become the best team in England in one year or 18 months. The target is this."
Chelsea now face the challenge of juggling European commitments with the domestic duties, Sarri's side heading to Greece to take on PAOK in their first Europa League group stage game on Thursday.
And Sarri accepted playing twice a week will mean he has to consider making changes to his team, with players including Ruben Loftus-Cheek in line for more minutes.
"Loftus-Cheek has a little problem with the right tibula," Sarri told reporters. "You saw today [Saturday] he wasn't able to play, but I hope he can recover in the next two or three days.
"Maybe it's an opportunity I can give him a chance. I don't know now because I want to have very clear the picture of the situation, who are the players that need to rest or not.
"Of course, Hazard or Pedro will rest on Thursday."
