Arsenal boss Mikel Arteta has accused officials of "changing the rules" after claiming Brentford's equaliser in the 1-1 draw at Emirates Stadium should have been ruled out for offside.
The Gunners had taken the lead in the second half when Leandro Trossard scored his first goal for the club.
But Ivan Toney levelled when he nodded in Christian Norgaard's cross from close range.
"I just looked back and it is offside, yes," said Arteta.
Toney's celebrations were delayed for a lengthy check by the video assistant referee (VAR).
Norgaard appeared to be offside in the build-up to the 74th-minute goal, while there was a suggestion Ethan Pinnock blocked Gabriel Magalhaes while in an offside position prior to that.
However, the decision to award the equaliser stood, leaving Arteta frustrated.
Ivan Toney scored his 15th goal of the season for Brentford against Arsenal, although Gunners boss Mikel Arteta felt it should have been disallowed for offside in the build up"The action when you get blocked when you are offside - you cannot block if you are offside," the Arsenal boss added.
"You have to apply certain principles in defending and you do that by sticking to the rules. Suddenly you change the rules and then you have to change your principles.
"So tell us before, so then you don't hide the line that high, because you're always going to have an advantage if you get blocked."
On the controversial strike, Brentford boss Thomas Frank said: "I agree that when they kicked the ball, Ethan (Pinnock) is in an offside position.
"Then, as far as I know the football laws, the next question is did he influence the cross? They decided it was not enough and I agree."
The point meant Arsenal are now six points clear of Manchester City, who play Aston Villa on Sunday and then visit the Gunners on Wednesday.
'Lost for words at VAR incompetency'
There was more VAR controversy earlier on Saturday when Chelsea were denied a late penalty against West Ham, despite Tomas Soucek appearing to block Conor Gallagher's shot with his arm.
The incident was checked but no further action taken.
"The early VAR decisions [were] absolutely ludicrous," said former Liverpool midfielder Danny Murphy. "I am lost for words at the incompetency of the people doing it.
"We are taking about poor decisions, minutes and minutes being wasted.
"Arsenal fans will be upset, the equaliser does look offside when it was headed it down."
