Mata has made just two starting appearances for Chelsea this season, leading to sections of supporters and the media to query why the twice-named club player of the season has not played more.
Instead, Mourinho has chosen the 22-year-old Oscar over Mata, 25, despite the Spaniard’s sensational form since arriving from Valencia in 2011, scoring 32 goals for the west Londoners.
And Mourinho refused to divulge on why exactly Mata does not fit into side currently, saying simply he must adapt his game.
He said: “There are things I can say with the players but not with you [the media]. The way I am reading the situation and the reasons why, in this moment, he is not playing so much are reasons I can only speak with him. These are football issues.
“He played against Everton from the beginning and you can analyse his performance, and he played against Basel, not like Demba Ba or John Obi Mikel to rescue the job, but when we were 1-0 up. He had specific tasks to do. He is part of a process, too.”
Mourinho admitted he is overseeing a change in Chelsea’s mentality. A revamp, so to speak, from the way the west Londoners have been playing since he left the club in 2007 and, even during his first spell at Stamford Bridge.
One of the main changes he is keen to make is the way he increases Chelsea’s attacking flair – an issue which Mata, according to Mourinho, must address.
“One thing is to play with Ramires and Oscar on the sides, with Mata playing in the middle behind the striker because he is a great talent. But another thing is to adapt with Oscar. He has great talent,” added Mourinho.
“In this moment, Oscar is my No 10 and, if somebody tells me that Oscar is not Chelsea’s best player since the beginning of the season, I’d have to disagree.
“I am not ready to play both of them. I want to build with Oscar as my number 10.”
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