The Times report that Willian has contacted Chelsea explaining that his absence is due to an issue with his passport, following an extended period off after the World Cup, he was originally expected to return to pre-season training last Friday.
And new manager Sarri is keen to resolve their situations in person with both having hinted at a desire to leave Stamford Bridge.
In case he leaves, Chelsea have to quickly complete the signing of another goalkeeper in the remaining days as their back-up options - Willy Caballero and Robert Green - are not up to the mark. "Or they would still have to sign a replacement next summer, but without getting a fee for Thibaut".
Jan Oblak and Kevin Trapp have been mentioned as alternatives but the Slovenian would cost £90m while Jack Butland, Pepe Reina and Kasper Schmeichel are other names to be linked.
"But, I hope that Courtois will be our goalkeeper".
"I am looking forward to playing in Wembley, it is my first time".
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This comes after the 29-year-old told Brazilian reporters that he was happy with life at Chelsea and in London.
The Blues No.1 has just a year left on his Chelsea contract and could be off to Real Madrid.
Chelsea ramp up their Premier League preperations on Sunday when the FA Cup holders face defending champions Manchester City at Wembley in the Community Shield (3pm).