Real Madrid announced that coach Zinedine Zidane has tested positive for COVID-19.
Zidane took part in Thursday's training session but did not take part in Friday morning's session ahead of Saturday's La Liga game at Alaves.
A club statement said: "Real Madrid announces its coach Zinedine Zidane has tested positive for COVID-19."
He will have to isolate for at least 10 days and will only be able to join the team once he has a negative test.
Madrid did not reveal whether Zidane in asymptomatic.
Zidane was on the bench in Madrid's shock 2-1 extra-time loss at Alcoyano that saw the team eliminated in the round of 32 of the Copa del Rey.
Earlier this month, Zidane, 48, had to isolate as a precaution after a member of his entourage tested positive for COVID-19 but tested negative then.
Zidane's assistant coach, David Bettoni, said on Friday: "I spoke with him this morning and he is absolutely fine."
There was much anticipation regarding Zidane's news conference following the disappointing week that Madrid has faced following last week's Spanish Supercup semifinal defeat to Athletic Bilbao and the shocking Copa loss to Spanish third division side Alcoyano.
Sources told ESPN that Madrid want to keep Zidane until the end of the season and that Zidane had no intention to resign.
Asked how Zidane is coping the pressure, Bettoni added: "The manager loves football and is fortunate to train this great club. It's a difficult time but he is sad not to be with us but he will be supporting us.
"I see him every morning with joy and a smile, with a desire to train. We are very eager to continue. We love this job and very happy to be here with these players.
"We had a good training session this morning. We are all together fighting to win and we have an opportunity tomorrow to prove this. We are ready to play a good game."
Meanwhile, Madrid also confirmed Fede Valverde has a muscle injury and is set to be sidelined for one month.