Switzerland coach Ottmar Hitzfeld is sweating over the fitness of Alexander Frei after his captain sustained an ankle injury on Wednesday.
Frei hurt is right ankle during a tackle on team-mate Steve Von Bergen in training, and spent several minutes on the ground before being taken to hospital for a scan.
Hitzfeld is now hoping the player has not suffered a serious injury which would rule him out of the World Cup.
He told Swiss news agency ATS: “I hope the ligaments are not damaged, that there is no fracture.
“He perhaps will not be ready for the first match but I will be able to call upon him after that.”
Hitzfeld also has concerns over the fitness of Valon Behrami ahead of next Wednesday’s World Cup opener against European champions Spain.
“If Valon can’t train at 100% by Sunday, he will not play in the first match,” Hitzfeld admitted.
The Swiss are 12/1 with Boylesports and Victor Chandler to upset the Spaniards, who are 3/10 (SkyBet) favourites. The draw is 9/2 (Bet365).