Mikel Arteta said that Arsenal cannot compete with Liverpool’s squad depth after watching his side surrender a 2-0 lead to Aston Villa to drop behind in the Premier League title race.

Two late goals from the substitute Darwin Núñez against Brentford stretched Arne Slot’s side’s lead to six points with a game in hand as Arsenal were pegged back by goals from Youri Tielemans and Ollie Watkins. Despite his side chasing a late winner, Arteta did not make a substitution until the 82nd minute when he brought on the Chelsea loanee Raheem Sterling, who was the only senior attacking option available.

Related: Ollie Watkins completes comeback as Aston Villa dent Arsenal’s title bid

The Arsenal manager refused to blame the video assistant referee’s decision to disallow Mikel Merino’s late goal for handball by Kai Havertz for his team’s shortcomings. But Arteta admitted that it had been frustrating to be able to make changes to his “physically drained” side, that has played three games in six days, once Villa had equalised.

“There are moments – obviously they managed to do that. They made the subs and the subs made the impact and they managed to change the game,” he said of Liverpool’s win over Brentford.

“In our side it was the opposite, even after conceding the two goals very close to each other. The danger was that I knew half the team could go downhill because we were physically drained. Suddenly, the team find another gear to go again and just put Aston Villa in there, in the box, and go and go again, trying to find the goal that we haven’t been able to score at the end.”

Asked whether it increased the importance of finding reinforcements for his squad this month, Arteta added: “Not the result, I think when you look at the performances, I don’t know how many teams are playing at this level in the league. When you look at the bench you probably say, we are very, very short.”

William Saliba missed the game due to a hamstring injury he picked up during Wednesday’s victory over Tottenham in the north London derby and Arteta revealed the France international will have further tests this week. Asked if he was worried about adding a vital member of his defence to the growing injury list, he said: “Yes for sure, especially with the numbers that we have in the squad and looking at our bench – very worried.”

Villa are now unbeaten in their last five matches and are just a point behind Chelsea in fifth spot. Unai Emery was delighted with the way his side responded to going behind.

“We showed resilience, we showed the mentality,” he said. “Today was a very good test. But we did a really fantastic job against a team that is challenging for the title and the Champions League.”