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Swiss captain Alexander Frei is a key player in the Swiss team, which is in Group H with Spain, Chile and Honduras. ((Philippe Desmazes/AFP/Getty Images))

Switzerland's team doctor says captain Alex Frei is undergoing "intensive" treatment for an ankle injury and it's unclear whether he'll recover in time for next week's World Cup match against Spain.

Frei sprained his right ankle during the team's final preparations before flying to South Africa.

Team doctor Cuno Wetzel told reporters Thursday the Swiss medical team is treating Frei with medications and physiotherapy, but it's too early to say how soon the 30-year-old striker can play.

Frei is a key player in the Swiss team, which is in Group H with Spain, Chile and Honduras.

Switzerland and Spain will be the last World Cup teams to enter the tournament when they play each other Wednesday.