Juventus defender Alex Sandro has tested positive for coronavirus, the Serie A club announced on Tuesday (AEDT).
The Brazil international - who played in Monday's 4-1 league victory over Udinese in Turin - underwent a test after displaying what Juve described as "mild symptoms".
Alex Sandro is self-isolating after it was confirmed he has contracted COVID-19, a concern for his club ahead of Thursday's huge showdown with Milan.
"Juventus announces that following the appearance of some mild symptoms, a check was arranged for the player Alex Sandro, which revealed his positivity to COVID-19," a statement read.
"The player has already been placed in isolation.
"The club is in contact with the health authorities for the definition of an effective implementation of the protocols needed to allow the training and competition activities of the team."
Alex Sandro featured for 83 minutes against Udinese before being replaced by Gianluca Frabotta, at which stage the hosts were 3-0 up in the game.
The 29-year-old has made seven league appearances under Andrea Pirlo during the 2020-21 campaign, as well as featuring three times in the Champions League group stage.
Juve travel to San Siro to face Milan - the unbeaten Serie A leaders - in midweek, followed by a home game against Sassuolo on Monday.