Willian had been on holiday following his global duty with Brazil at the World Cup, but he was due to report back to Chelsea's camp on time with the Blues expecting him to play some part in Wednesday night's friendly against Arsenal.
"I am very happy at Chelsea and I am very happy living in London".
"I don't know. At the moment Courtois is the goalkeeper of the club, of Chelsea", Sarri said.
"I want to win, because it is very important to have a trophy immediately".
"I spoke yesterday with him about him being late, not his future", Sarri told a news conference on Friday.
Alvaro Morata and Olivier Giroud remain at the club and with Willian, Eden Hazard and Pedro all risky in the final third, Chelsea should cause problems for several other defenders.
When asked if he was confident that Willian would stay in West London, Sarri replied: "Yes".
'It depends especially on him I think.
Maurizio Sarri is unimpressed with Willian after the Chelsea winger returned late for pre-season training.
Of course, that includes key duo Eden Hazard and Thibaut Courtois, who helped Belgium to third-place out in Russian Federation.
"I am looking forward to playing in Wembley, it is my first time".
When asked whether the whole situation was unusual, he added, "I think so".
'It is understandable people might be upset because he wants to leave the club, we accept that.
Chelsea play Manchester City in the Community Shield on Sunday (15:00 BST).