Xherdan Shaqiri has become the third Liverpool player to test positive for coronavirus over the past seven days.
Reds players left the club on Monday to join up with their national teams, as domestic football takes a break for 10 days.
But the Swiss FA confirmed on Tuesday morning that Shaqiri had tested positive for Covid-19.
A statement read: “Xherdan Shaqiri has tested positive for Covid-19. In consultation with the health authorities, he is in isolation.
“The strict protective measures and requirements of UEFA for national teams in accordance with the ‘UEFA Return to Play Protocol’ have been strictly adhered to since the move began.
“Based on this, clarifications are currently underway with the local health authorities about how to proceed.”
Shaqiri will now withdraw from international duty. He will miss the friendly with Croatia and Nations League games against Spain and Germany.
Swiss star forced to self-isolate
The 28-year-old, who had been tipped to leave the club on deadline day, will now have to self-isolate for 10 days.
That timeline does, however, mean he should be fit for the Merseyside derby at Everton on October 17.
Sadio Mane then followed suit on Friday, having missed training at Melwood after also testing positive.