Maurizio Sarri believes Chelsea need up to one year to reach the level of Premier League leaders Liverpool.

Despite only taking over from Antonio Conte in the summer, Sarri has overseen a positive start to the season with five Premier League wins and a Europa League victory so far this term.

However, Chelsea's trip to the London Stadium to face city rivals West Ham on Sunday saw the Blues drop their first points of the season after they were held to a goalless draw by Manuel Pellegrini's side.

Liverpool, meanwhile, maintained their winning start to the campaign with a 3-0 victory against Southampton on Saturday which saw the Reds open up a two-point lead over Chelsea and holders Manchester City.

Sarri's men now take on Liverpool twice in the space of a week as they first play the Reds in the League Cup at Anfield on Wednesday night before hosting them in the Premier League three days later.

And despite Chelsea's good start to the season, Sarri believes his team are not yet at the same level as Liverpool - but could be within a year.

When asked whether the Liverpool clash at Stamford Bridge is a must-win game in order to keep up the pace in the title race, Sarri told reporters: "Must win, in football, doesn't exist.

"We have to play against a very, very good team. Against a team who have worked with the same coach for three or four years – I don't remember exactly.

"They are a step forward of us at this moment. We have started to work all together 35/40 days ago and, 40 days ago less 10 for the international break, so for us it's a bit early.

"We have to work then, maybe, in one year we will be at the same level as Liverpool."

Liverpool's attack-minded play has seen the team score 17 goals in seven matches in all competitions this term and Sarri admitted playing a team that likes to go forward won't be easy.

"Easy, against [Mohamed] Salah, [Roberto] Firmino and [Sadio] Mane? I think it is impossible. It will be really a very difficult match. Maybe a spectacular match but, for us, very difficult I think."

Sarri also added that he will make changes to his team that plays Liverpool in the League Cup, saying: "They [Liverpool] have played yesterday and have one day's more rest than us.

"I want to see the picture of the situation tomorrow morning during the training session. Now, really, I don't know. Maybe I will have to change 11 players, maybe only five. At this moment, I don't know."