The Brazilian playmaker has been linked with a switch to Stamford Bridge for some time, with transfer rumours first emerging last summer.
The Blues were then reported to have seen a big-money bid rejected during the winter window.
Roberto Di Matteo remains keen to do a deal for the talented 23-year-old, who has spent the last five years with Shakhtar.
Lucescu claims the club would be prepared to sanction a sale if the right offer comes along, but has informed Chelsea that they will need to dig a little deeper if they are to get their man.
"I told Willian he can leave, but only if the right offer is made," Lucescu told Dolce Sport.
"He's a great player. Willian was the biggest investment Shakhtar have made in a young player, we have to respect that. He played only seven or eight games in Brazil."
Chelsea have already spent a reported £32million on Belgian forward Eden Hazard this summer, and Lucescu claims they will have to get closer to that figure if they are to land Willian.
"They paid a lot of money for Hazard but are not willing to pay for Willian, even though he's better in my opinion," he added.
"Chelsea want to buy Brazilian but made an offer for the eastern European market. They offered €34million but we don't think that's his current value."