Chelsea suffered a shock 2-1 defeat against Wolves at Molineux on Wednesday night and that loss has left the Blues a massive 10 points behind Premier League leaders Manchester City.
England international Ruben Loftus-Cheek had put the visitors ahead in the first half but strikes from Raul Jimenez and Diogo Jota after the break ensured Nuno Espirito Santo's men picked up a much-needed victory.
Sarri's men, who sit fourth, welcome the Citizens to Stamford Bridge on Saturday and the Italian tactician effectively ruled his side out of the title race this season.
He said after the match: "Manchester City are in another category. We have to play and fight for the top four. It is a very difficult result for the top four."
The Chelsea boss also criticised his side for being over confident in the loss to Wolves, adding: "After this match we are less confident but maybe it's better because sometimes my players show me that they have too much confidence.
"I am really very worried, not for the result but the fact that after the first goal we conceded we did not react very well. I am really very worried for this, not for the result."