The Selecao legend has backed the South American rivals to play in the showpiece occasion on July 13, but admits that it would be a disaster if his country failed to win.
"I'm pretty sure that the final will be Brazil-Argentina," he told reporters. "It will be a dream if we win. But to lose would be a nightmare. So hopefully Argentina lose before then."
Ronaldo was part of the Brazil squad that won the World Cup in 2002.