Arjen Robben's World Cup hopes will depend on the outcome of a scan after he was injured during the Netherlands's 6-1 friendly win over Hungary.
Robben, who hobbled off two minutes from time, has not travelled to South Africa with the rest of the Dutch squad.
"My first thought was this can't be true, the end of the final warm-up match, everyone is fit and then this," said coach Bert van Marwijk.
"We now have to wait. I can replace Robben until 24 hours before our opening match but as long as there is hope he recovers in time he will stay in the squad."
The Dutch open their campaign on June 14 against Denmark.