Steve Cooper hit out at the officiating after Manchester United's Harry Maguire escaped a red card at the City Ground.
Maguire went into the book early as United took on Cooper's Nottingham Forest, and home players and fans appealed in numbers later in the first half when the ball struck the centre-back's arm in the penalty area. Forest believed they should have been awarded a penalty, while their manager queried whether the England international should also have picked up a second yellow for the offence.
In the end, it was neither a penalty nor a red card, with VAR not overruling the on-pitch decision. It proved costly for the relegation-threatened hosts, who fell to a 2-0 defeat through goals from Antony and Diogo Dalot.
"Harry Maguire's was a definitely penalty (for handball)," Cooper told Sky Sports. "Then a second yellow card and red. A terrible decision.
"How have VAR not picked up on that? Another call and apology from them then, which won't help."
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"The Harry Maguire one, for me, is a really poor error," he added. "The referee should see it and I understand why he hasn’t because of the amount of players and the angle, but why VAR haven’t is not right in my opinion.
"It’s another big moment that is going to have scrutiny on VAR and obviously there’s been a lot of not positive decisions over the past few weeks. It’s not the reason why we lost the game - although it could have been a penalty and a second yellow for Harry Maguire, we could have scored the penalty and gone one up.
"I’m not gonna sit here and say it’s the reason why we didn’t win today but it does [have a big impact] to be fair, I’m biting my tongue here because I don’t want to use this as why we’re in the league position we’re in and why we’ve lost the game - it’s not - but for me it’s a bad error."
The defeat leaves Nottingham Forest in 18th place, though they are only in the bottom three on goal difference. Fellow relegation battlers Everton were beaten by Fulham on Saturday, While 16th-place Leeds face Liverpool on Monday night.
Next up for Cooper's side is a trip to Anfield on April 22, followed by a midweek game at home to Brighton. They also still have to face league leaders Arsenal, taking on Mikel Arteta's team in their penultimate match of the season.