The game at the City Ground ended 1-1, with both bosses left frustrated.

Cooper said: "We all want referees to be in a good place. But they have just raised more questions than answers."

On Saturday, the referees' body the Professional Game Match Officials Limited (PGMOL) admitted the decision to disallow Luis Diaz's goal in nine-man Liverpool's 2-1 loss to Tottenham Hotspur was "a significant human error".

At 0-0 and with the Reds a man down, Diaz's goal was ruled out following an unusually quick Video Assistant Referee (VAR) check by Darren England, in which the customary offside line graphic was not shown.

England had been due to be the fourth official at the City Ground, but was stood down following that error and replaced by Craig Pawson.

Niakhate was sent off early in the second half for two bookable offences, the second of which saw the defender catch the heel of Yoane Wissa, with the decision being given after a VAR check.

"Honestly, if he doesn't give him a second yellow, nobody mentions it," added Cooper. "All of your colleagues on TV and radio have said the same.

"With it being the only Premier League game of the day, the PGMOL needed a real clean day and unfortunately they have got the opposite.

"I'm annoyed with the first yellow, he shouldn't have lunged in. The second yellow, of course it was accidental. You need football understanding to see that. It's a contact game.

"We all want referees to be at the right level and help them but they have to help themselves. The last thing they needed was talking points about refereeing decisions.

"This league is amazing, but every part of it needs to be at the top level."

Brentford scored immediately after the red card through Christian Norgaard's header, only for Nicolas Dominguez to equalise for Forest seven minutes later.

'I'm tired of talking about VAR'

However, Frank, whose side have now not won in five successive league matches, was unhappy about the refusal to give his team a spot-kick.

Frank thought Wissa was fouled early in the second half by Forest goalkeeper Matt Turner, who caught the Brentford man in his follow-through.

The Bees also had two other penalty appeals turned down,.

"I'm tired talking about VAR," said Frank. "I just want to talk about good performances.

"The two handballs, some managers would claim them as penalties, I won't, but I would really hate it if they were given against me.

"The Wissa one is a clear penalty though. You can't go through the man, so unfortunately that's a mistake from VAR.

"Unfortunately our players are too honest. Maybe they need to be nasty, but I would never say that to the players - I like honest players.

"I know it's the talk of the town, VAR. I'm just so tired of talking about it, I'd much rather talk about football.

"I also feel the pain and frustration when it doesn't go your way. I need to focus on what I can affect."

Asked about the potential penalties, Cooper added: "I honestly don't know what is handball and what isn't. Last Monday it needed someone to say this is what it is. I don't think anyone knows."

'Trust a big thing going forward'

Speaking after Saturday's game at Spurs, manager Jurgen Klopp said Liverpool's defeat came in "the most unfair circumstances" with "crazy decisions".

The Reds also had Curtis Jones and Diogo Jota sent off - both decisions that Klopp disagreed with - and lost to a stoppage-time Joel Matip own goal after resolutely keeping Spurs out.

Klopp added: "If you want to change, you have to do without our voice. If we say something we get fined. They didn't do it on purpose but if we want to talk about it, do it properly."

Reds skipper Virgil van Dijk admitted he was losing faith in VAR after Saturday's costly officiating blunder,

Former England striker Alan Shearer, who also agreed Jones' red card was harsh, described VAR's error as "incomprehensible" on Saturday's BBC Match of the Day.

He said: "A horrendous day for the officials and VAR. We have seen some howlers but that is the biggest. Trust is going to be a big thing going forward."