AC Milan were forced to cancel a training session on Saturday after head coach Stefano Pioli tested positive for coronavirus.
Pioli was "promptly placed in quarantine" after the club's latest round of medical checks at the weekend, with the rest of the squad subsequently granted an extra two days off before returning to the training pitch.
The Milan boss is asymptomatic, and all other tests undertaken returned negative results.
A club statement read: "AC Milan announces that Stefano Pioli has tested positive following a quick test carried out this morning.
"The health authorities have been informed, and the coach, who is currently showing no symptoms, has gone into quarantine at home.
"All other tests carried out by the squad and staff came back negative.
"As a result, today's training session has been cancelled. Training ahead of the match with Napoli will resume on Monday, subject to the checks set out in the federal protocol."
Pioli is the latest in a growing number of Milan figures to have contracted the illness, with first-team quartet Zlatan Ibrahimovic, Daniel Maldini, Matteo Gabbia and Leo Duarte also having taken in spells in quarantine after posting positive Covid-19 tests at the start of the season.
Despite those health setbacks, Milan are sitting two points clear of surprise package Sassuolo at the top of Serie A at the moment, and are unbeaten in 19 league matches.
Pioli's men have picked up five wins from their opening seven fixtures, scoring 16 goals while only letting in seven at the other end of the pitch.
Milan are scheduled to face Napoli at Stadio San Paolo next Sunday, where they will be aiming to get back to winning ways after being held to a 2-2 draw by Hellas Verona at San Siro before the international break.
The Italian giants are due back in Europa League action four days later, with a trip to Stade Pierre-Mauroy to face Lille on the cards, before preparations begin for another domestic clash against Fiorentina on November 29.