Shakhtar Donetsk coach Mircea Lucescu has slapped a €35 million price-tag on Willian.
Manchester City and Tottenham are both chasing the talented Brazilian.
But Lucescu warned: "There is a sale clause and that is €35 million.
"Chelsea paid €31 million this summer for Oscar. The difference between Oscar and Willian is that Willian is much more mature and has a lot of Champions League experience.
"The Blues wanted him this summer for €20 million, but we refused."