The Fulham forward believes the unfancied central American nation have been placed into the 'Group of Death' at next summer's finals in Brazil.
Not only will they have to tackle England, they will also lock horns with four-time winners Italy and 2010 semi-finalists Uruguay.
Costa Rica are considered to be rank outsiders to make the knockout stages, but Ruiz feels an underdog standing could work in their favour as they will be free to play without pressure.
He said in the Daily Mirror: "It could hardly be more difficult or complicated for us, two great European sides and the 2010 semi-finalists.
"Yet at the same time it will be a real treat for us to play against them.
"I am looking forward to the summer very much and I am filled with optimism.
"All of us know we have a golden opportunity to transcend all the expectations, to shine, and to earn applause and international acclaim for what we could do."
Ruiz added: "Yes, we are in the group of death, the hardest of all. That is simply a reality we have to face.
"Compared to England, Italy and Uruguay, we are the ugly ducklings of the group, the weakest team, the easiest. But we know we can surprise all of them."