Benfica goalkeeper Mile Svilar has tested positive for COVID-19, the club said on Sunday, and three players from their rivals Sporting have also been infected.
Benfica confirmed in their medical bulletin that Belgian Svilar, 21, will miss the Champions League third round qualifier away to PAOK in Greece on Tuesday.
The match will be Benfica's first of the new season and their first since coach Jorge Jesus, who won three league titles in a previous six-year stint at the club, returned to the helm.
A club source at Sporting confirmed to Reuters that three players had tested positive, had been isolated and were asymptomatic. The players were not named.
The source said a friendly against Napoli later on Sunday would probably be cancelled.
Sporting's first game of the season is at home to Gil Vicente on Saturday.
(Reporting by Catarina Demony; Writing by Brian Homewood, editing by Ed Osmond)
