The Football Association is investigating Crystal Palace's Eberechi Eze over an apparent Covid-19 breach.
Eze, who moved from Queens Park Rangers last year, was in the directors' box at the Kiyan Prince Foundation Stadium for Saturday's FA Cup third-round tie with Fulham, played behind closed doors.
The FA did not approve the visit and "will be looking into the matter".
"He accepts it was an error of judgement to attend the match," Palace said in a statement.
"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.
"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 the latest in a series of Covid-19 stories involving Premier League clubs.
Crystal Palace captain Luka Milivojevic issued a public apology after he was pictured breaching Covid-19 rules on New Year's Eve, mixing his household with Fulham forward Aleksandar Mitrovic and his family.
Southampton's match with Shrewsbury Town was postponed because of a Covid-19 outbreak at the League One club, while Aston Villa were forced to field a youth team against Liverpool after an outbreak forced the first team into isolation.
Newcastle manager Steve Bruce has described the continuation of Premier League football as "morally wrong" with the country in lockdown and stricter protocols being imposed across the Premier League.
- All the goals and highlights from a huge Saturday of third-round matches are streaming now on BBC iPlayer