Brazil's Health Regulatory Agency, ANVISA, was a victim of a cyber attack on Wednesday which included an Argentina flag and a provocative message after last weekend's World Cup qualifier in São Paulo between the two countries was abandoned.
Sunday's fixture was halted after seven minutes as Brazilian health officials stormed the pitch over alleged Covid-19 quarantine breaches by the visitors, triggering a meleé involving team officials and players.
The officials intervened just hours after health authorities in Brazil said four England-based players in Argentina's squad should be placed in "immediate quarantine" for breaching Covid-19 protocols.
"ANVISA, we didn't quarantine before walking all over your servers: are you going to send us off too?" the message on a black background on ANVISA's website read.
The hack on the site, where foreign travellers must fill in a form before arriving in Brazil, was out of service for around 90 minutes but none of the regulator's other systems were affected.
According to ANVISA, Premier League players – Giovani Lo Celso and Cristian Romero of Tottenham, and Aston Villa's Emiliano Martínez and Emiliano Buendía – provided "false information" upon entering Brazil. They had allegedly failed to disclose that they had recently spent time in Britain.
Brazil, where Covid-19 has claimed more than 580,000 lives, denies entry to foreigners who have visited the United Kingdom, South Africa or India within 14 days prior to their scheduled arrival.
On Monday, football's governing body, FIFA said possible disciplinary action would be taken "in due course" after the incident.
The controversy came after Premier League clubs refused to release nine Brazilians to play for their country in the World Cup qualifiers over coronavirus rules that would have required them to quarantine on their return to England.
The Brazilian football association (CBF) confirmed to AFP it had asked FIFA to invoke regulations that bar players for featuring for their clubs for five days after an international break if they are not released by their domestic outfits.
Liverpool trio Alisson Becker, Fabinho and Roberto Firmino, Manchester City's Ederson and Gabriel Jesus, Fred of Manchester United, Chelsea defender Thiago Silva and Leeds midfielder Raphinha look set to miss out this weekend if the clubs comply.
Speaking Wednesday, Brazil's national team coach Tite said "not everything is allowed" in football in reference to the aborted World Cup qualifier.
"The justice system, laws, respect and social order exists; in football not everything is allowed, there are rules," said Tite, without explicitly mentioning Argentina, during a press conference in Recife ahead of Brazil's upcoming match with Peru.
"I don't know exactly what was done nor at what point. I cannot and should not judge, but to go above the law... no. A bit of respect for an entity, for a country, for a population, for a club and a national team," said Tite. "I still want the game to be played, but if a mistake was made then the law applies."
South American football's governing body CONMEBOL said the game had been "suspended" but gave no detail on whether the match would be played at another date.