Vicente del Bosque's side won their first World Cup in South Africa three years ago and they will be among the favourites to lift the trophy again next year.
But with Brazil beating them in the final of the Confederations Cup over the summer and Italy regulars in the latter stages of major tournaments, Mata is wary of the difficulty Spain face in their quest to retain the trophy.
He told Laureus.com: "I think it’s going to be really, really hard to win this tournament because obviously some of the countries that are going to be there are also really fighting to make it to the final.
"For me Brazil, the hosts, have a great, great squad with young players. They beat us in the Confederations Cup last summer. Italy are also going to really fight with us for the title."
Much is made of Spain's technical brilliance and attractive brand of football, but former Valencia man Mata has revealed that the spirit in the squad is also key to their success.
"Talking about our national team, Spain, to be honest, it’s going to be very special for me to be there (the World Cup)," he added.
"I feel so lucky to be training with such a team because we know each other really well. We know how to play because we are friends off the pitch, it’s very important.
"If you are a team that wants to win you have to be like a family. I think that’s what we are in the Spanish team. Probably that’s one of the secrets that the Spanish have.
"Playing in the World Cup is the greatest experience for any player. I had the opportunity to play in South Africa and win our country's first ever World Cup, so it will be fantastic to be part of that team again.
"We are facing a big challenge: to be world champions again and keep writing history. And it will be a dream come true to play and win a World Cup and in Brazil, a country that loves football."