La Liga side Valencia have said more than a third of their playing and backroom staff have tested positive for the coronavirus but that all cases were currently asymptomatic.
The club had reported five cases of COVID-19 on Sunday, with Argentina's Ezequiel Garay and France's Eliaquim Mangala both confirming they were among those who had contracted the virus.
"Several further tests for the COVID-19 coronavirus amongst Valencia coaching staff and players have come back positive," the club said in a statement.
Valencia travelled to Milan last month for a Champions League match against Atalanta, which was played in front of a packed San Siro stadium, before restrictions were placed on sports events in Italy -- the worst-hit country in Europe.
"Despite the strict measures adopted by the club after their Champions League game ... these latest results show the exposure inherent to such matches has caused a positive test rate of around 35%," Valencia added.
"All cases are asymptomatic and those involved are currently isolated at home, receiving medical assessment and carrying out their scheduled training plan."
The flu-like virus has wiped out the international sporting calendar, with the big five soccer leagues in Europe -- England, Spain, Germany, Italy and France -- as well as the Champions League and Europa League all suspended.
The coronavirus has infected almost 180,000 people and killed over 7,000 worldwide.
FIFA's Infantino urges unity, calls for FAs to push WHO advice
FIFA is urging all football associations to publicise the World Health Organization's preventive measures against the spread of the coronavirus, Gianni Infantino, president of world soccer's governing body, said in a letter to its members on Monday.
Ahead of Tuesday's meeting of European soccer's governing body UEFA, which will see calls for this year's European Championship to be postponed, Infantino also called for unity in dealing with the impact of the pandemic on the game.
The FIFA chief said his organisation will use its social media and other channels to help popularise WHO advice about hand-washing, avoiding close contact and staying at home when showing symptoms of the virus.
In the letter, a copy of which was seen by Reuters, Infantino urged football associations and others in the game to follow suit.
"In partnership with the WHO, we are launching awareness building initiatives designed to provide practical recommendations and steps to tackle the spread of COVID-19," he said.
"I highly recommend you to also at your level use the power of football to send out and spread these key messages."
The FIFA president said the game had a responsibility to keep those involved in football as healthy as possible.
"Under these circumstances, we must now do everything in our power to protect fans, players, coaches, and everyone else involved in our beautiful game. Most importantly, the football authorities must take all necessary measures to prevent the virus spreading to the wider community," he said.
Most football leagues in Europe and many around the world have suspended play due to the spread of the virus and European governing body UEFA are meeting on Tuesday to discuss a possible postponement of Euro 2020.
Should the pan-continental Euros be moved to 2021 it could come into conflict with FIFA's plans for an expanded Club World Cup in that timeslot involving the world's leading club sides.
There is widespread uncertainty about how to finish domestic and international seasons and many clubs, leagues and federations are certain to face short-term losses in revenue.
But Infantino said it was vital the game stayed together in dealing with the problems.
"Thus far, the world football community has shown a sense of solidarity and unity in the face of this threat and we should continue to do the same when thinking about how we will address the consequences we will have to face for the future of our game, once this serious risk to human health is behind us," said Infantino.
"FIFA will keep in regular contact with all relevant stakeholders during this difficult period and look to find in due course solutions in a spirit of cooperation, taking into account the interests of football at all levels."
FIFA studying coronavirus impact on schedules, player contracts
World soccer governing body FIFA said on Monday that it was looking into the potential impact postponed fixtures would have on player contracts after the coronavirus outbreak suspended leagues across Europe and the rest of the world.
The big five leagues in Europe -- in England, Spain, Germany, Italy and France -- have all been suspended, as have the Champions League and Europa League, adding to a potential fixture pile-up should the competitions resume later this year.
However, many players whose deals run until the end of the season will be out of contract after June 30, raising questions over how the ongoing league season can be completed with the current squads.
"FIFA is analysing the current situation and the potential impact it may have on all areas of football. More information will follow in due course," a FIFA spokesperson told Reuters.
Teams such as Chelsea, who are chasing Champions League qualification, could be affected with front line players Olivier Giroud, Pedro and Willian all on contracts expiring on June 30.
The off-season transfer window is also set to open when the season ends, casting doubt over whether players will be allowed to move on before the current season reaches a conclusion.
The 24-team Euro 2020 tournament, scheduled to be held in 12 countries from June 12 to July 12, could also be pushed back a year which would create a longer window for national leagues to finish their seasons.
UEFA is being urged to prioritise domestic competitions and pressure is growing for Euro 2020 to be postponed, with representatives of European clubs and leagues joining national federations on an emergency video-conference call on Tuesday.