The match saw three penalties awarded, two of which were for Fulham -- the first given for a Nélson Semedo challenge on Tom Cairney, and as well as a late João Gomes challenge on Harry Wilson after a VAR review.
"I've been in to see the referee," O'Neil said. "He regrets the fact that he wasn't sent to the screen to overturn the first penalty. He doesn't think it is a penalty because he thinks he should have been sent to the screen and he would have overturned it from the images that we watched together in his room.
"We then had an interesting discussion around the two possible red cards. They've sent somebody out to speak to one of my staff and said by the letter of the law, Tim Ream should receive a second yellow card and should be sent off.
"We then discussed the headbutt, which it was, but he debated that a little bit with me as well and he said that it was a soft headbutt. Which I just said that that's crazy. He's absolutely crazy. So we can headbutt people as long as it's deemed soft or not hard enough? So my son at home watching that -- millions of children watching that -- we're telling them that you can headbutt people on a football pitch, as long as it's not too hard?"
O'Neil's side have been on the losing end of three VAR decisions this season that the Premier League's Independent Key Match Incidents Panel has admitted are errors -- these include a missed foul by Manchester United's André Onana in their opening match, while Newcastle United and Sheffield United were both given penalties which should have been overturned, the latter spot kick being scored 10 minutes into stoppage-time to give them the victory.
Wolves are 12th in the Premier League with 15 points from 13 games, but O'Neil said after Monday's defeat that "bad refereeing decisions" have now cost them up to seven points.
"We're probably seven points down on PGMOL reviews, depending on what they come back with this time," he added. "So that's the difference between 22 points and 15 on my reputation at a big club, trying to build as a new manager. The difference between 15 and 22 is irreparable."
"Maybe with just a human referee one of the penalties may have gone against us, but the fact that we have conceded two, for me VAR is not helping with subjective decisions. Maybe tonight has finally turned me against VAR."
Information from Reuters contributed to this report.