José Mourinho has warned Juan Mata he will remain on the periphery of the Chelsea first team until he adapts his game to fit the new manager's style, with Oscar considered the side's first-choice No10 for the foreseeable future.

In a wide-ranging critique of his Chelsea side, Mourinho said he was unhappy with their recent style and said the players must adapt to his demands. "I don't like the way Chelsea were playing the last couple of years; the club doesn't like it and we want to change," he said. "We want to play a different style. The past is history – even my past. I'm here like I've just arrived."

Mata, Chelsea's player of the year in each of his two seasons at the club, was an integral member of the side who won the Champions League in 2012 and followed that up with last season's Europa League success, playing 64 times for the London club last term. Yet he has featured only three times to date under the Portuguese and was substituted on each of his two Premier League starts, as he attempts to adapt to a wider role having lost his favoured playmaker berth to Oscar.

The 25-year-old's absence had previously been explained by his involvement in the summer's Confederations Cup and a subsequent minor injury, which had served to disrupt his pre-season preparations. Yet, with tentative interest from Paris Saint-Germain and Manchester United having been knocked back over the summer, Mourinho has now confirmed the player still has work to do if he is to be considered key, with the Spain international expected to start on the bench against Fulham on Saturday as Chelsea attempt to end a four-game winless run.

"The way I'm reading the situation and the reasons why, in this moment, he's not playing so much are things I can speak about with him, but not publicly," Mourinho said. "But he played against Everton from the start and you can analyse his performance. And he came on against Basel when the team were winning 1-0 – not like Demba Ba or Mikel John Obi, who came on to rescue the game –with specific tasks to do.

"It's part of a process with him, too. It is one thing to play with Ramires and Oscar closing down opponents on each side, and Mata as a No10 behind a striker with his clever assists, clever passes and fantastic actions because he has great talent. But it is another thing to adapt to the way we want to play. In this moment, Oscar is my No10 and, if anyone tells me Oscar has not been Chelsea's best player this season, I'd have todisagree. I have to prove to the fans that I am good. Now [Mata] must do the same."

Mata, Oscar and Eden Hazard featured regularly last season as an attacking trident behind a lone forward, and there remains the scope for that trio to be restored. "But only when [Mata] adapts to what we want," Mourinho said. "I'm not ready to ask Oscar to track opposing full-backs. Brazil has more talented players in the No10 position than any other country in the world, and he plays there for the national team, so I want to build with Oscar as my No10. I want the other two players, from the side, to adapt to that reality and learn how to do things they were not ready to do before.

"The players are open to some of the changes, and not so open to others because this is more difficult. If I'm a defender I want to play low block, with no space behind me. If I'm an attacking player I'd prefer to play without a position, without certain responsibilities, and with others behind me to cover so I don't need to worry about [tracking back]. It's about changing mentality. It takes a bit of time. But it won't take five, six, seven years. I promise."