Switzerland's team doctor has revealed it is too early to tell if captain Alexander Frei will be fit to face Spain.
The 30-year-old striker sprained his right ankle before the team flew out to South Africa and is now undergoing intensive treatment on the knock.
Doctor Cuno Wetzel revealed on Thursday that it is not known if Frei will recover in time to play the European champions on Wednesday.
Frei is regarded as a key player for the Swiss, as the skipper has earned more than 70 caps for his country.
Switzerland have been drawn in Group H for this summer's showpiece tournament, and take on Chile and Honduras as well as Spain.