Valencia's Argentinian defender Ezequiel Garay is the first La Liga player to test positive for the coronavirus.
Valencia wrote a statement on Sunday which explained the club had five confirmed cases of club members having tested positive for the virus. The club then revealed on Monday that 35% of its playing and support squad had tested positive.
Garay, 33, who underwent surgery to repair an ACL injury last month, announced on Sunday on social media he is in isolation. He posted a photograph on Instagram, smiling and giving a thumbs-up with the message: "It's clear that I started 2020 on the wrong foot.
"I've tested positive for coronavirus, I feel very well and it's now a case of following what the health authorities recommend, for the time being to be isolated."
La Liga declared last week that Spain's first and second divisions had been suspended for at least the next two rounds because of the coronavirus outbreak.
Real Madrid players have been in quarantine since Thursday after one of the club's basketball players tested positive.
Spain, the European country with the second-highest number of cases after Italy, called a state of emergency on Saturday.