The world and European champions head to South America as one of the favourites for the tournament, but the Real Madrid keeper is expecting a tough competition.
"We have a difficult group. In addition, our first two matches are against [Netherlands and Chile] who, in theory, we will be vying for qualification with," Casillas told reporters.
"I think we need to go to Brazil without any pressure. In these last six years we haven't done good things, we have done sensational things. We have earned the right to fail.
"We are going with the idea of competing and defending our title but we know that there are 31 other teams who want to do the same and it won't be easy."
La Roja kick off their campaign against the Netherlands on June 13.