The Costa Ricans get their finals campaign underway against China on 4 June and Guimaraes said he has already decided 80% of his line-up for the game.
And the coach said he is hoping to make "two or three changes" against the US in their final warm-up which he hopes will help "sharpen up his side".
"After the match, everything should be completely clear," said Guimaraes, a Brazilian-born and naturalised Costa Rican.
Guimaraes played under China coach Bora Milutinovic during Costa Rica's World Cup run in 1990 when the Ticos reached their only finals.
And he is expecting the veteran coach to be well prepared for the Group C clash.
"He'll probably even use mathematical equations in this World Cup," Guimaraes said.
Striker Paulo Wanchope, who had surgery on his right knee seven months ago and is still receiving therapy, missed training on Wednesday.
But the coach reassured journalists that he would suit up on Thursday.
"Paulo will not be the problem," Guimaraes said. "He'll probably be ready for the friendly game with the United States."