PREM: Chelsea v Cardiff preview
Chelsea are one of three Premier League teams to have registered four wins from four matches, alongside Liverpool and Watford.
Asked which teams are in title contention, boss Maurizio Sarri said: "At the moment I can answer Man City or Liverpool, at the moment.
"We need another step, I think, to be the same level.
"It's very difficult. The gap was 30 points at the beginning of the season."
Cardiff have picked up just two points from their opening four Premier League games and are one of five teams still without a win.
Things don't get much easier with this trip. In fact, Cardiff's only league win in the last 55 years against the Blues was at Stamford Bridge in 1981.
Cardiff manager Neil Warnock wants to sign Chelsea and Wales teenager Ethan Ampadu on loan in January.
Warnock says he will speak to Chelsea officials about the prospect of signing Ampadu on loan in the next transfer window.
Midfielder Ampadu, who celebrated his 18th birthday o Friday, shone for Wales against the Republic of Ireland and Denmark during the international break.
"I will be speaking to somebody at Chelsea about one or two things," Warnock said. "I think they should loan him (Ampadu) to us and I could help him as well.
"He doesn't look out of place. What I like about him is that he is so confident."
Maurizio Sarri will make a late decision on the fitness of players who returned from international duty. Cesc Fabregas is returning to full fitness but won't be ready to play this weekend.
Emerson Palmieri, Davide Zappacosta and Ruben Loftus-Cheek have had knocks which could see them miss out.
Cardiff City's Josh Murphy (hamstring) and Aron Gunnarsson (knee) are back in the squad for the trip to Stamford Bridge. However, Nathaniel Mendez-Laing remains a few weeks away from returning with a knee injury.