Arsenal manager Mikel Arteta questioned a decision by match officials, saying Ivan Toney's equalizer for Brentford in their 1-1 Premier League draw on Saturday should have been ruled out for offside.
New signing Leandro Trossard scored his first goal for Arsenal but the north London club were left frustrated as Toney levelled after nodding home Christian Norgaard's cross.
The equalizer cleared a lengthy VAR check but Arteta felt Ethan Pinnock appeared to be offside while blocking Gabriel Magalhaes as a free-kick was delivered into the area for Toney to volley back across goal.
"I just looked back and it is offside, yes," Arteta said. "Have they explained why it wasn't allowed? No.
"You have to apply certain principles in defending and you do that by sticking to the rules. Suddenly you change the rules .
"So tell us before so then you don't hold the defensive line that high. Because you're always going to have an advantage if you get blocked. You cannot block if you are offside."
Arsenal have 51 points, six more than Manchester City, whom they host on Wednesday.
Tottenham boss Antonio Conte was back at the helm after missing last weekend's 1-0 win against City following surgery, but his side were humiliated 4-1 away to Leicester.
Graham Potter admitted Chelsea are still "a work in progress" after their winless run extended to three games as Joao Felix's first goal for the Blues was cancelled out by Emerson in a 1-1 draw at West Ham.
In France, Monaco punished a PSG decimated by injuries to Kylian Mbappe and Lionel Messi to register a 3-1 victory, led by captain Wissam Ben Yedder's first-half double and assist.
In Germany, Bayern powered to a 3-0 win over Bochum to stay a point clear atop the Bundesliga as they warmed up for Tuesday's Champions League match with PSG.
Christian Norgaard gives Ivan Toney the cross that saw Arsenal drop points.
