In a statement, the club said the virus spread among the squad following last month's trip to Milan, "an area confirmed as 'high risk' by the Italian authorities days afterwards", for the first leg of their Champions League last-16 tie against Atalanta.
"Despite the strict measures adopted by the club after its UEFA Champions League game against Atalanta on February 19th in Milan -an area confirmed as 'high risk' by the Italian authorities days afterwards-, which included maintaining a distance between the squad and club employees/the general public, these latest results show that the exposure inherent to such matches has caused a positive test rate of around 35 per cent," the statement read.
"We also wish to express our confidence in our healthcare system and the recommendations by the Ministry of Health for those cases of coronavirus infection being treated with isolation," it added.
On Sunday, the club had announced that five of the club's players and staff had tested positive for coronavirus, including defender Ezequiel Garay.
Major football leagues in Spain have all been suspended indefinitely to contain the spread of coronavirus, which has claimed over 6,000 lives across the world. In Spain, more than 300 people have lost their lives so far.