The former Castilla star declared: "The juniors at those big teams are treated unfairly. There is a lack of opportunities and it is a pity.
"For me, it is the youth who must form the backbone of teams for their sentiment, dedication and devotion to those colors that they have always defended."
Mata also had a kind word for the much-maligned Ronald Koeman.
"Ronald was the one who gave me confidence and continuity. He arrived in a delicate situation and bet on a young boy. So I am very grateful."