Portugal face Sweden in a Nations League group game on Wednesday, but Cristiano will miss the game as he immediately started the quarantine and recovery process.
Other members of the Portugal squad have tested negative for Covid-19.
In a statement, the Portuguese Football Federation (PFF) said that Ronaldo is ‘doing well, without symptoms and in isolation.”
Portugal, winners of the inaugural (2019) Nations League, played out a goalless draw against France in Paris on Sunday and are top of the group, level on points with France.
PSG forward Neymar Jr. and AC Milan striker Zlatan Ibrahimovic are some of the other football stars who have tested positive for Covid-19.