A previous Wolves complaint about referee Lee Mason prompted "humiliating" criticism from Nuno Espirito Santo following December's game at Burnley, according to an independent disciplinary panel.
The Wolves head coach was fined for post-match comments in which he questioned whether Mason had the "quality" to be a Premier League official, following the 2-1 defeat at Burnley on December 21.
In published written reasons, the panel concluded Nuno "went into the game with a certain level of animus" after Wolves reported Mason in the aftermath of their 1-1 draw against Newcastle on October 25.
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The panel heard how Wolves felt the complaint resulted in Mason's temporary demotion to the Championship for a short time, with Nuno expressing "his surprise and unhappiness" at the "subsequent appointment to the fixture against Burnley".
The panel unanimously concluded that the criticism "would have been utterly humiliating" for the official, and warned that public criticism of a referee could have a serious effect on mental health, "even for those as experienced as Mr Mason".
They added behaviour such as Nuno's contributes to a climate where match officials are viewed as "fair game" and can "create a perception that such conduct is acceptable at all levels of the game".
According to the panel, Nuno launched an "opportunistic attack on the professional competence of Lee Mason" after he told Sky Sports "the referee does not have the quality to whistle in a game in the Premier League".
The panel said the words were "wholly unsolicited by the interviewers".
However, the three-person commission acknowledged that Nuno "deserves credit" for his prompt admission of the charge and "what appears to be a genuine apology, in general, and to Mr Mason".