Willian is thrilled to be playing under Maurizio Sarri after coming close to leaving Stamford Bridge following a row with former Chelsea boss Antonio Conte.
The Blues start their Europa League campaign at PAOK on Thursday having won their first five Premier League games under Conte's replacement.
Willian made no secret of the breakdown in his relationship with Conte, previously saying there was "no chance" he would have stayed at the club had the Italian not left.
The Brazil international memorably posted a photo of Chelsea's FA Cup celebrations with trophy emojis covering up Conte, which he later blamed on his daughter.