Granit Xhaka missed Switzerland's 2-1 friendly win over Greece on Wednesday after testing positive for Covid-19.
"Xhaka was diagnosed with symptoms on the morning of the game and was immediately isolated in his room," read a Swiss Football Association statement.
Switzerland face Italy and Northern Ireland in September's World Cup qualifiers.
They play the European champions on 5 September before travelling to Belfast's Windsor Park three days later.
The Swiss FA confirmed that local health authorities had said no further measures were needed for the team because the other players were all either vaccinated or had previously recovered from the virus.