The 25-year-old former Valencia player has started just two Premier League games this season.
Mata told Chelsea's website: "I'm not the kind of man that gets down. I always believe in myself and train really hard. This is my way to behave, to be positive as much as I can. I have really enjoyed playing for this club in the last two seasons. I know what I can give to the team and I'm just trying to do that."
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