The Blues were heavily linked with the 24-year-old in January while André Villas-Boas was still in charge of the west Londoners.
And Di Matteo, who took over from the Portuguese coach following his dismissal in March, says he is still a big fan of the attacking midfielder but does not know where his future lies.
“As an assistant [at the time] I wasn’t involved in those conversations but Willian is a fantastic player with good qualities,” said Di Matteo.
“We have a good squad with good players and I don’t know where his future is, but the way he is playing here he looks quite happy.”
Di Matteo’s comments come after Shakhtar Donetsk boss Mircea Lucescu hit out at the Blues for undervaluing Willian during their January pursuit of the player.
“Willian was far away from Chelsea,” he said. “They didn’t even get anywhere near to our requirements, having done nothing to make my promises to Willian come true.
“Speaking specifically about the amounts, they officially offered the sum for which we had bought him young.
“I would really like them to highly appreciate his true value tomorrow and realise that they made a big mistake.”
Willian has also been linked with a move to Tottenham in recent days.
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