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.