Germany midfielder Marco Reus has been diagnosed with a partial ankle ligament tear, although he is still set to fly out to Brazil with his team-mates with no replacement as yet called up.
The Borussia Dortmund midfielder picked up the injury just before half-time in Germany's 6-1 win over Armenia on Friday night.
He was taken to hospital immediately for a scan with the results - a partial ankle syndesmosis tear - announced during the night.
The 25-year-old is expected to miss the World Cup, although Germany coach Joachim Low has nine days to decide whether or not to replace him in his squad. Changes can be made up to 24 hours prior to the first group game.
"I hope I don't have to make any changes and that Marco is fit enough," Low told ZDF television on Thursday night.
Such an injury can take up to two months to recover from, effectively ending Reus' hopes of representing his country in Brazil.
Schalke duo Leon Goretzka and Max Meyer are the most likely candidates to be called up to replace Reus. They were both involved in a 10-day training camp in South Tyrol before being struck off Low's final squad selection.