Granit Xhaka has sustained a knee injury less than three weeks before Switzerland begin their World Cup campaign against Brazil.
The Arsenal midfielder hurt his left knee during a training session on Thursday and received treatment from his national team's medical staff.
There were reports the player was taken immediately to hospital, but the Swiss Football Association (SFV) denied that was the case.
"[Team doctor] Pierre-Etienne Fournier explained that Granit Xhaka was feeling pain on the outside of his left knee," it confirmed in a statement.
"This issue will be examined in more detail and as soon as possible through an MRI scan. Further information will follow as soon as a more concrete diagnosis is available."
Xhaka appears unlikely to feature in Switzerland's friendly with Spain on Sunday or the game against Japan next Friday. His chances of facing Brazil on June 17 would also seem to be in doubt.
The news is a major blow to head coach Vladimir Petkovic, given Xhaka is a key component in his midfield plans.
He played 11 times in their World Cup qualifying campaign, including in both legs of the play-off win over Northern Ireland in November.
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