The Spain international was one of the club's standout performers last season, scoring 12 goals and providing as many assists in 35 Premier League appearances.
But he has found himself on the periphery of the first team this season, with new boss Jose Mourinho overlooking the 25-year-old on several occasions, including last Saturday's 2-0 victory over Fulham.
Speaking to The Sun, Mata said: "I've been training hard but it's not the same. You improve your rhythm by playing games.
"I've worked hard and wanted to show everyone that I can play and everything is OK.
"It is easy for me to focus on football and just do what I have to do. The only thing I have in my mind is to keep working, keep training hard, keep improving and keep scoring and making assists. That's what I did.
"I've played in three positions. In the beginning I was playing as a left winger, then on the right and last season as a number 10. I feel comfortable playing in any offensive position.
"It's better if a player can play in lots of positions rather than just one."
