Nottingham Forest have been charged with improper conduct by the Football Association over their extraordinary statement about VAR Stuart Attwell, on the day referee analyst Mark Clattenburg quit the club.

Forest issued a social media post minutes after the defeat to Everton on April 21 criticising the rejection of three penalty appeals, and claiming they had warned referees’ body Professional Game Match Officials Limited (PGMOL) that Attwell was a fan of relegation rivals Luton but nothing was done about it.

The FA has also charged Forest boss Nuno Espirito Santo and full-back Neco Williams over their comments about the officiating, while issuing a formal warning to Clattenburg hours after he announced his resignation.

The FA alleged the comments by Forest, Nuno and Williams “constitute improper conduct in that they imply bias and/or question the integrity of the match officials and/or bring the game into disrepute”.

The club, Nuno and Williams have until May 9 to respond, the FA said.

The Premier League is also investigating the Forest post on Attwell under its rules, having put out a statement saying it was “extremely disappointed” by it.

Despite that, Forest doubled down and issued a further statement urging PGMOL to consider “contextual rivalries” when making match appointments.

Earlier this week PGMOL chief refereeing officer Howard Webb admitted Attwell should have advised on-field referee Anthony Taylor to check the third of the appeals – for a challenge by Ashley Young on Callum Hudson-Odoi – on the monitor.

Webb said there would probably have been “a different outcome” if that had happened.

Nuno was asked after the Everton game whether he thought it was appropriate for the club to complain about the appointment of officials before a match, and said: “I prefer not to answer if it is appropriate.

“It’s a feeling and trying to avoid what happened today and not raise any more suspicions or thoughts that no one wants. It is about preventing.”

Forest defender Williams told Sky Sports he thought any of the top six teams would be “getting every single one” of the penalty claims.

Earlier on Friday, Clattenburg announced he was leaving his consultancy role, saying he had felt he had become “more of a hindrance than a help” to Forest and that offering his services to the club had led to “unintended friction” between the club and “other participants”.

Even before the Everton incident, Clattenburg had spoken to journalists in the mixed zone after Forest’s defeat to Liverpool to highlight the error in law made by referee Paul Tierney in awarding a drop ball to the Merseysiders when Forest were in possession.

He wrote in the Daily Mail that the decisions made by Taylor and Attwell in the Everton game were “mind-boggling” to watch.

“Why Attwell did not send Taylor to his screen, only he will know.”