Crystal Palace have said that they will address Eberechi Eze's trip to QPR for their FA Cup game with Fulham, where he was pictured without a mask.
The Football Association will reportedly investigate the apparent transgression.
"QPR have acknowledged they made a mistake in hosting Eberechi Eze in the directors' box ... without our knowledge," Palace confirmed in a statement posted to their official website.
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"Whilst we recognise Eberechi's desire to support his former team mates, he accepts it was an error of judgment to attend the match.
"We were also concerned to see pictures of Eberechi not wearing a mask at certain moments and are speaking to him about these apparent lapses, which will be dealt with internally."
It is not the first time a Palace player has landed in trouble for breaching Covid-19 protocols. Captain Luka Milivojevic apologised for breaching guidelines after attending a party on New Year's Eve.
The Premier League recorded 36 new Covid-19 cases last week amid growing pressure from managers to pause the season in which five top-flight matches have been postponed since December. Liverpool boss Jurgen Klopp has said that the league should continue while Sam Allardyce has called for a two week 'circuit breaker.'
207 players and staff have returned positive results for the coronavirus in 21 rounds of testing since the start of the current season.
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The English Football League (EFL), which governs the three divisions below the Premier League, said there were 112 positive cases in their latest round of testing.
British media reported that new EFL Chief Executive Trevor Birch had written to clubs stressing the importance of safety protocols, saying teams must take action against those who breach the rules.
"We all understand the scrutiny the game remains under and we will come under extreme governmental pressure if we continue to flout the rules and guidance in place," he was quoted as saying in the letter.
The government has allowed elite sport to continue despite the country being placed into lockdown amid a surge in COVID-19 cases. More than 80,000 people have died in the UK due to the virus.