Chelsea are looking to hijack Tottenham's bid to land Willian, with the Blues reportedly in advanced talks with the Brazilian playmaker.
Willian was thought to be on the verge of completing a £30 million ($46.7 million) move to Spurs after reportedly passing a medical, but is now considering his options after Chelsea showed their interest.
Reports in the U.K. suggest if Willian signs for Chelsea, then it will cast a serious doubt over Juan Mata's future.
Mata was reportedly used in a player-plus-cash offer for Wayne Rooney earlier this summer, a claim which Chelsea vehemently denied.
However, reports have persisted over Mata's future with Jose Mourinho reportedly preferring the likes of Eden Hazard and Oscar for the central playmaking role.
Mata has been Chelsea's best player over the last couple of seasons, and it will be difficult to fathom how Willian will be seen as an upgrade to the classy Spaniard.
If Mata is indeed sold, it is not likely to go down too well with the Chelsea faithful. Willian is a much more pacy player than Mata and is equally adept at playing in the wings as behind the frontman.
While Mata did not play a single minute of the opening English Premier League game against Hull City, the Spanish international did start the game against Aston Villa on Wednesday - Mata has been struggling with a couple of niggles according to Mourinho.
Mourinho has insisted Mata is not for sale, but it remains to be seen whether the Portuguese will consider selling the 25-year-old to Manchester United as part of a deal which would bring Mourinho's No.1 target of the summer - Rooney - to Stamford Bridge.
David Moyes is desperate to land a central midfielder this summer and has failed in bids to bring Cesc Fabregas from Barcelona.
Luka Modric is also seen as an option, but Real Madrid are now unwilling to sell following the loss of Xabi Alonso through injury.
