LONDON -- Chelsea are reluctant to sell Willian in January because they fear doing so could damage Maurizio Sarri's chances of a top-four finish, sources have told ESPN FC.
Reports on Thursday claimed Chelsea had rejected an offer worth £50 million from Barcelona that would see Willian's fellow Brazil winger Malcom move to Stamford Bridge.
Sources have told ESPN FC it would take a significant cash bid for Chelsea to consider parting with Willian, regarded by Sarri as a key first-team player.
Speaking at a news conference on Friday, the coach said it would be "impossible" to lose Willian, and the club are keen to ensure he is as well-equipped as possible for what is set to be a close battle for a top-four spot.
Barcelona made a concerted effort to sign Willian in the summer, and sources close to the player have told ESPN FC that he believes they remain interested.
He has 18 months left on his Chelsea contract and has yet to begin talks about an extension.
Sarri's wing options have been bolstered by the return to fitness of both Willian and Pedro from muscle injuries, but uncertainty surrounding Callum Hudson-Odoi's future makes Willian's availability all the more important.
Earlier this week, sources told ESPN FC that Chelsea were prepared to report Bayern Munich to FIFA if evidence of an illegal approach to Hudson-Odoi was found.
The winger, who came through the Chelsea ranks, currently has no intention of signing a new contract at Stamford Bridge as Bayern await a response to their fourth bid, understood to be in the region of £35m.
Bayern sporting director Hasan Salihamidzic said on Wednesday that the Bundesliga champions "absolutely want to sign" Hudson-Odoi, and sources have told ESPN FC that they are increasingly confident of completing a deal.
Chelsea, however, have not given up hope of changing Hudson-Odoi's mind, and on Friday Sarri accused Bayern of a lack of respect by making their interest public.
Information from ESPN Brasil's Joao Castelo-Branco was used in this report.