Belletti, 36, who scored the winning goal for Barca against Arsenal in the 2006 Champions League final, enjoyed a successful three-year spell in Catalunya between 2004 and 2007.
La Roja lifted Euro 2012 on July 1 to add to their World Cup 2010 and Euro 2008 triumphs, but the former Fluminense full-back credited those results to the Catalans.
"If not for the Barca players, the Spanish team would not be what it is today. If they win the 2014 World Cup they will surely be the best team of all time," he told Futbolnet.
And Belletti also gave his backing to new Barca coach Tito Vilanova, and tipped his former club for success in 2012-2013.
After a missing out the Liga title to Real Madrid and suffering Champions League defeat to Chelsea last season, the Brazilian backed Pep Guardiola's successor as the right man to get the Camp Nou outfit back to winning ways.
"It's nice having someone who knows the project from inside out leading the team," he added.
"Although it will be difficult to maintain this sequence of titles and there will be comparisons [between the two coaches], we must remember that the bedrock of the team are the players."