Granit Xhaka has tested positive for Covid-19, the Swiss federation announced on Wednesday.
The Arsenal midfielder was left out of the squad to face Greece on Wednesday after showing symptoms earlier in the day.
A PCR test produced a positive result, ruling Xhaka out, while a member of Switzerland's backroom staff has also gone into quarantine.
What was said?
"Xhaka was diagnosed with symptoms on the morning of the game and was immediately isolated in his room," the federation said in a statement.
"A quick test turned out negative, the subsequent PCR test, carried out to be on the safe side, produced a positive result in the evening.