Referees' chief Howard Webb said "tunnel vision" from VAR Matt Donohue led to Manchester City's derby winner being allowed to stand -- but that the assistant VAR should have intervened.
Erling Haaland's goal was given after a review in Sunday's match against Manchester United at Old Trafford.
Donohue and assistant VAR Blake Antrobus correctly determined Haaland was onside, but failed to recognise Enzo Fernández was interfering with play in an offside position as he dived forward in an effort to head in Joško Gvardiol's cross.
The decision to award the goal has caused uproar, and even to calls for VAR to be scrapped altogether, with Donohue and Antrobus stood down by Pro Ref for this weekend's Premier League matches.
Webb, the chief refereeing officer at Pro Ref, said on the "Match Officials: Mic'd Up" programme which aired on Tuesday: "I was really disappointed with this outcome. We all are. None more so than the officials themselves.
"They take a lot of personal pride in what they do and they're obviously hurting now, having fallen short in this situation. They'll not be officiating again until after the international break.
"We've reached out to Manchester United and acknowledged the error, as we do when these things happen.
"They don't happen that often, but we want to ensure that we are transparent and open, and we've played the audio and the footage to the football club to let them know what happened, and we're going to review this situation to understand what elements of process fell down in this situation which meant we didn't get to the right outcome."
Webb said Donohue was too focused on whether or not Fernández had touched the ball, rather than considering whether he was interfering.
- Ogden: Manchester derby mess shows VAR's quest for perfection is doomed to fail
- Manchester derby reaction: City's 10-man master class
- VAR review: Decision behind Manchester derby goal explained
"In that moment, he [Donohue] gets tunnel vision," Webb said.
"He gets focused on Haaland, and it's down to the rest of his team to pull him out of that tunnel, and unfortunately, that didn't happen on this occasion.
"When you watch it casually, you think, 'Well, this is obviously offside against Fernández'.
"When you're sat in that chair, and you've got other things going through your head in relation to the process that you need to follow to establish Haaland's position, to follow through the attacking phase of play, you can get that tunnel-vision sort of effect.
"We've seen that before. We've put processes in place that protect us from that, with the assistant VAR stepping in to pull the VAR out of that tunnel, but it didn't happen on this occasion.
"This goal should have been disallowed. And highly unfortunately, it wasn't, and we'll review it, reflect upon it, and try to take the learning forward to prevent this unusual type of error from happening again."
United head coach Michael Carrick said it was "worrying" that the goal had been allowed to stand, while ex-United striker and BBC Match of the Day pundit Wayne Rooney said he was "baffled" by the decision.
Webb said referee Michael Oliver was right to send off City midfielder Phil Foden for a kick out at United's Bruno Fernandes earlier in the same game.
There have been suggestions Fernandes should also have seen red after he kicked Foden while the England man was on the ground, but Webb said: "It is more petulant than violent. To be violent conduct, it has to have excessive force or brutality, and when you look at that, particularly in full speed, it doesn't have those elements. So therefore, this would be a yellow card offence."
Webb explained that there was no option for the VAR to recommend a yellow for Fernandes because the referee saw, and sanctioned, the red card challenge by Foden on the field.
Webb says Maguire, Williams decisions correct
Webb also said the officials followed the right process in allowing a goal for United against Ipswich in match week two to stand, and in disallowing a Neco Williams goal for Nottingham Forest against Tottenham.
United's second goal against Ipswich on Aug. 30 was given because a Harry Maguire shot deflected in off Jacob Greaves. If it had gone straight in, the goal would have had to be disallowed for accidental handball.
Webb described the law which penalises accidental handballs when they occur immediately before a goal is scored as "a bit of a nonsense", adding: "I think we ought to look at this and just allow the officials to determine whether it's a normal handball offence [regardless of whether a goal directly results or not].
"Did [Maguire] make himself bigger? Did he deliberately handle the ball? And I don't think he does those things in this situation."
Forest full-back Williams fell foul of the same law after his arm was judged to touched the ball as he bundled it over the line against Spurs for what would have been the winner in their match on Sept. 5.
"So the VAR looks at it, initially you can hear that he's not conclusive," Webb said.
"But then when he slows it down to an appropriate pace and gets the right angle, you can see that the ball clearly and conclusively hits that right arm.
"It's clear. It's conclusive, and the goal has to be disallowed."
