Speaking at his post-match news conference on Tuesday night, Sarri said: "Chelsea v Tottenham is a very hard match and also for them, so it will not be easy to win at Stamford Bridge but after this performance, if we are able to play on the same level I think that we can do it".
"Of course if he was to go to another club then we need a replacement", he said.
"But at the moment he is here, he has to think only to play".
Sarri declined to comment on his apparent pursuit of the Napoli striker Gonzalo Higuaín, who is on loan at Milan from Juventus, but he did say that if Álvaro Morata departed, with loan moves to Sevilla and Atletico Madrid mooted, Chelsea would have to recruit a striker.
"There are 300 players involved in the market and they need to think only to the next match otherwise it is impossible to play".
Chelsea will be without Ruben Loftus-Cheek for the Newcastle game as the midfielder deals with back pain, while Sarri confirmed that Cesc Fabregas would not be considered for selection as he waits to complete a move to Monaco.
"At the moment, for his mental condition, he's not able to play".
"The rest is up to him and his brother, his agent, who's talking to Leonardo, and I hope that he stays for as long as possible".
"Willian for us is really very important".
Willian was on Thursday linked with Barcelona, but Sarri ruled out the prospect of the Brazilian departing this month.
Meanwhile, Chelsea FC are now preparing for their home Premier League clash against Newcastle United at Stamford Bridge on Saturday night.
The Blues lost to Tottenham in their Carabao Cup semi-final first leg on Tuesday and Sarri admitted to having a far-than-ordinary superstition. We need to improve in attacking the spaces.