Eberechi Eze's visit to his former club QPR on Saturday for their FA Cup third-round tie against Fulham is being investigated by the Football Association, with manager Mark Warburton going on to admit it was the club's "error" for accepting the player's request.
The winger, who joined Crystal Palace from QPR for £20m in the summer, sat in the directors' box at the Kiyan Prince Foundation Stadium as Rangers were beaten 2-0 in extra-time by Fulham.
It is understood Eze's attendance was conditional on him complying with Covid-19 protocols and returning a negative coronavirus test. He complied with all of these.
The FA has told Sky Sports News it will be looking into Eze's attendance and the governing body has stated that, contrary to some reports, it did not grant the 22-year-old approval to go to the game.
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Eze was pictured not wearing a facemask as he watched his old team slip to a defeat.
"We know the situation that society is facing in this country, we are all very aware of it," said Warburton ahead of QPR's match at Luton on Tuesday.
"QPR as a club have stringent protocols in place that we apply very strongly to every single player and staff member. On this occasion, we should have declined the request. It's as simple as that. We made the error.
"Eberechi is an outstanding character. I can't speak highly enough of him. He made a request, we should have said no. On this rare occasion, we have made a mistake, it's as plain and simple as that. It will not happen again."
A Crystal Palace statement read: "QPR have acknowledged they made a mistake in hosting Eberechi Eze in the directors' box at Saturday's FA Cup match against Fulham without our knowledge.
"Whilst we recognize Eberechi's desire to support his former team mates, he accepts it was an error of judgement 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."
Palace boss Roy Hodgson this week made it clear to his players that no further breaches of Government coronavirus guidelines will be accepted after captain Luka Milivojevic breached the rules on New Year's Eve.
Milivojevic issued an apology on Wednesday after his household mixed with Fulham forward Aleksandar Mitrovic and his family.