Chelsea boss Andre Villas-Boas confirmed his side's interest in signing Willian over the weekend.
Shakhtar have now confirmed to Sky Sports News that they have rejected a €20million bid for Willian.
"We have no burning desire to sell the player, but in football some things are impossible to avoid," Shakhtar CEO Sergei Palkin was quoted as saying in Monday's Daily Mail.
"If it weren't for our good relationship with Chelsea - and Willian does not hide his intention to test himself in one of the best clubs in the English Premier League - we would insist on the £29m release clause written into the player's contract.
"It is important to understand that we are talking about Chelsea's desire to buy Willian, but not Shakhtar's desire to sell him."