Switzerland are sweating on the fitness of captain Alexander Frei after he limped out of training.
The FC Basel striker was grounded by a tackle from team-mate Steve von Bergen and had to be helped away by medics as he injured his ankle.
The Swiss are now awaiting results of scans to confirm the extent of the damage.
Switzerland are due to fly to South Africa on Wednesday evening, ahead of their opening game with Spain next week.
Coach Ottmar Hitzfeld is now nervously awaiting the results.
"I hope he has not torn any ligaments or fractured anything," said Hitzfeld.
"We have sent Alex to hospital to get a clear diagnosis.
"At the moment, I presume that he will be able to fly with us. You have always got to think positively.
"Although he had a lot of pain, we have got to hope that he can play in the tournament, even if he cannot play in the opening game."
"I hope that he is fit again soon, and I believe he will be."
Hitzfeld also refused to blame Von Bergen for being over-zealous in his tackle.
"We are preparing for a World Cup and you have got to have tackles," he said.
"The players have got to train hard, at a high pace and of course you risk injuries.
"We are preparing for the games against Spain, Chile and Honduras and we need a certain level of intensity."