Onyedinma is banned from Saturday's game at Sunderland after two yellow cards at home to Blackburn Rovers.
The first was for going into the crowd to celebrate, the second for waving an imaginary card at referee Bobby Madley.
Madley admitted he was wrong to show the first card, with the forward pushed towards the stands by surging team-mates, but dismissals for two cautions cannot be appealed.
"In my office I was lucky to have Howard Webb (head of the Professional Game Match Officials Board), Kevin Friend (in charge of Championship officials) and the referee from last weekend Mr Madley, talking through the weekend," revealed Miller manager Matt Taylor, who did not ask for it.
"The apology, which we've had two weeks on the bounce now, was for the first yellow card.
"We'll lobby the FA to be able to appeal yellow cards, especially when they are said to be a mistake. Referees don't want teams punished on a double basis."
It goes both ways.
"I've had meetings with the team to say out of 11 yellow cards this season, (only) five have been for physical actions," said Taylor. "We need to change quickly.
"But they (the PGMOL) are open to our feedback and want to be better. It's for the collective benefit of the game but as managers our conduct has to improve."
Shane Ferguson has had a hernia operation in Germany. Taylor did not know the extent, but said it would not impact recruitment.