Costa Rica midfielder Harold Wallace faces a race against time to be fit for Sunday's match with Turkey.
Wallace, 26, injured his groin against China and
coach Alexandre Guimaraes has
insisted he needs players who are fully fit for the crucial match in Incheon, South Korea.
Costa Rica beat China 2-0 in their opening game and victory against Turkey would put them in a strong position to qualify from Group C, which also includes Brazil.
"I have said it before and today I say it again - those who will
play are the ones who are at maximum fitness," Guimaraes said.
"We are looking at solutions based on Harold not being there,
but we will wait on the doctor's decision."
Wallace took part in a shortened training session on Thursday including a
programme of special exercises to test the injury.