The Chelsea attacker feels the strength of Spain's top two teams is harming the league, and may more cause players to leave the country in the search of top honours
The 24-year-old won the Champions League and FA Cup in his first season with the west London outfit, following a summer move from Valencia.
And he insisted it would have been "impossible" to win silverware with his former club, admitting he fears that top players outside of the Spanish giants will also have to leave Spain.
"I'm a little worried to see so many players leave the Spanish Liga, for the competitiveness of the league," he told France Foot.
"We have two teams fighting for the title, and the third, for four years, ends 30 points [behind] the champion.
"If you don't play for Real or Barca, you can't win a trophy.
"Today, it's impossible for my former club Valencia to win the championship. This cannot be good for Spanish football. Supporters of other clubs also suffer."
However, despite suggesting that the financial dealings of some Spanish clubs may be less transparent, the playmaker believes La Liga is still the best in the world along with the Premier League.
"In England, clubs must prove they can pay wages of players before the start of the season," he added.
"Accounts of Spanish clubs, it is sometimes complicated. But the Liga stays the best league in the world, with the Premier League!"
Mata also revealed his delight at having won trophies so soon with Chelsea, but added it was hard work rather than luck that brought his new team success.
"It was my first season in England and [success] arrived very quickly. I immediately found my marks with my team-mates. I had the chance to score a goal in my first game and after that I enjoyed myself," he continued.
"I came to Chelsea because I wanted to win trophies, and for my first year, I won two trophies, with the first Champions League of the club's history. I said: 'how can you be so lucky?' - because if you work a lot, it is often an opportunity that makes us a winner."
The Spaniard went on to hail the influence of his compatriots on English football and, although he has been left out of Vicente del Bosque's latest squad, looked ahead to the upcoming clash with France.
"We offer something different than what people expect of English football, which is very physical. Spanish football has a great period with all these trophies, which we enjoy," he said.
"We want Spanish players in other major championships, and suddenly we discover other [styles of] football - that is a means to progress."
"The France team stays one of the best teams in the world. And when we play against one of the best teams in the world, we want to show that we are better."