Serie A sides have been worrying about the results of their routine coronavirus tests amid a nationwide spike of positive cases that signals a resurgence of the pandemic in Italy.
The count of positive footballers in the top-flight was reported at 32 on Thursday, with 11 of 20 teams in isolation, as more than 7,000 new cases and 43 deaths were reported by the country's health authorities.
In a week marked by international games ahead of the top-billed Milan derby set for Saturday, Cristiano Ronaldo's positive test at the camp of the Portugal squad was a bad blow for Juventus - who went in isolation after the positive test of midfielder Weston McKennie.
Ronaldo on Wednesday returned by ambulance flight to his Turin residence, hoping to soon be available by returning a negative test.
The title holders visit promoted Crotone on Saturday.
Meanwhile, with six quarantined players, Inter Milan are the second worst hit after Genoa, who with 10 reported cases count a third of the Serie A total.
Nerazzurri coach Antonio Conte has defenders Milan Skriniar, Alessandro Bastoni and Ashley Young in isolation with midfielders Radja Nainggolan and Roberto Gagliardini, plus reserve keeper Ionut Radu, while Stefano Sensi is suspended.
Conte found comfort from his footballers' good showings in international action, where Belgian Romelu Lukaku struck three times in two Nations League fixtures, while Denmark's Christian Eriksen was twice on target and Argentina striker Lautaro Martinez scored a classy goal in a World Cup qualifier.
Milan's good news came from ace Zlatan Ibrahimovic, who will be fit for the derby after returning a negative test on Friday, but defenders Mattia Gabbia and Leo Duarte remain in isolation.
The big match finds the Devils on nine maximum points, sitting second on goal difference behind Atalanta, with Inter on seven along with Juve and Sassuolo.
Also on Saturday, Napoli welcome Atalanta after a sports judge handed them a 3-0 default defeat, and docked them a point, for not showing up against Juventus on October 4.
The Neapolitans have appealed against the ruling, claiming that health authorities prevented them from travelling to Turin, following the positive cases of Piotr Zielinski and Eljif Elmas, who remain unavailable.
Lazio, who like Juve, Inter and Napoli open the Champions League campaign next week, are at Sampdoria on Saturday in a match without positives.
Sunday's Torino v Cagliari is also virus-free, unlike the regional derby between Bologna and Sassuolo, Spezia v Fiorentina, Udinese v Parma and Roma v Benevento.
Genoa, who in early October recorded a peak of 17 positive footballers, are gradually returning to normality and should visit Verona on Monday.