Chelsea, Sky Blues manager Pep Guardiola has confirmed.
Sarri, who has not won a trophy in his career, said: "The match for us is very hard for one reason: they have worked all together for two years. I'm so happy he came here".
Guardiola said his team wanted to win the Community Shield to get their season off to a flying start but admitted they would not better last season's results in the Premier League. "If, at the end, we decide to bring in another one it will be because they can be a special player for the future, not to have one more player for the numbers".
'So, I don't know. "I think we have played against a good team in Arsenal and we could see the way we want to play", the defender said. "I want to win, because it is very important to have a trophy immediately".
And keeping Chelsea's leading talents is the priority. He reported late for Chelsea duty after the World Cup.
Sunday's clash is an highly-anticipated one as it pits Maurizio Sarri and Guardiola against each other for the first time since the Italian manager has taken charge in West London. It was a very positive conversation.
"There is not a Willian problem", Sarri said.
Considering Chelsea will also be without Thibaut Courtois, N'Golo Kante and Eden Hazard, it's pretty much an even field for both sides.
The 26-year-old has a year to run on his current contract and has been continually linked with a move prior to the summer transfer window closing, with Real Madrid rumoured to be his most likely destination if he is sold. A lot depends on him and us.
In each of the past two Community Shield matches, new signings have scored, with Zlatan Ibrahimovic netting for Manchester United against Leicester City in 2016 and Sead Kolasinac doing likewise for Arsenal previous year.
Sarri admits City are also hindered by players absent on post-World Cup breaks, but the situation contrasts with Chelsea's as he is new to the role.