O’Neil spoke about the referee in disparaging terms after his team lost 2-1 to Manchester City earlier this season.
The young coach had stated that unconscious bias may have played a part in a late goal being contentiously awarded against his team.
O'Neil said after the game: “There's no chance people are purposely against Wolves, let's be clear.
“But is there something in the subconscious around the decision making - without even knowing it are you more likely to give it to Man City than Wolves?
“My senses are heightened when we are facing Man City, are the officials the same? When it's (Erling) Haaland and Man City is there something in there that, not on purpose, influences decision making?
“They guarantee me there isn't. But they are human and Man City scoring a last-minute winner is a big thing, a bigger thing than Wolves scoring a last-minute goal against West Ham.
“If I had to upset someone in the street and there's a big and little guy in the street, I'm upsetting the little guy.”
While O’Neil has been reprimanded by the Football Association, he has escaped punishment.