Mata joined United in January from Chelsea.
"I will always be grateful to Chelsea," he told the Daily Mail. "To the directors, the owner and the fans, because from the first day to the last they were fantastic.
"I wish them the best, I really do. I have a lot of friends there. Cesar (Azpilicueta), Fernando (Torres), David (Luiz), Oscar. I talk to Lampard and Terry a lot too. I was with them for two and a half years and I wish them the best."
He is proud of the open thank you letter he wrote Chelsea fans when he left.
"I didn’t do that just for the sake of my image, it was heartfelt. I wanted to express what I felt about Chelsea, about the fans, who had always treated me so well."
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