The goalkeeper believes La Roja's main rivals are becoming stronger but says he is relishing the prospect of playing in "the cradle of football" this summer
Last year's 3-0 defeat to Brazil in the final of the Confederations Cup has raised questions over Spain's chances of successfully defending their World Cup crown this summer, despite La Roja having won the last two European Championships as well as the title in South Africa in 2010.
And back-up goalkeeper Reina believes it is getting tougher for Vicente del Bosque's side to maintain their dominance on the international stage.
"We're going to try to become world champions again but we know that it's going to be difficult," Reina was quoted as saying by AS.
"Other teams are catching up to us and it just keeps getting more difficult."
Reina has been part of Spain's all-conquering squads at Euro 2008 and 2012, as well as at the 2010 World Cup.
But the 31-year-old, who spent last season on loan at Napoli from Liverpool, has admitted that playing in the finals in Brazil will be a truly special experience.
"This World Cup is a bit of an obsession for me because it is going to be really special," Reina added. "We'll be playing in the cradle of football."