Arsenal had a forgettable night as they not only wasted an opportunity to restore their six-point lead at the top of the Premier League but also saw Kai Havertz suffer an injury blow.
Mikel Arteta's team were held to a 1-1 draw at Brentford on Thursday with Noni Madueke's second-half header cancelled out by Keane Lewis-Potter.
It dampened the mood in the dressing room after it emerged that Havertz is likely to be ruled out of the north London derby against Tottenham.
Havertz had only recently returned to full fitness following hamstring and knee surgeries which had sidelined him for the best part of a year.
However, reports have emerged Havertz is set to be sidelined due to a muscle injury.
The Germany international is likely to miss the FA Cup fourth-round tie against Wigan on Sunday, as well as the Gunners' visits to Wolves and Spurs in the Premier League next week.
Havertz has made just seven appearances so far after he suffered a knee injury in Arsenal's win at Manchester United on the opening weekend of the season.
Things did not improve on the field for Arsenal. Brentford were the better side in the first half but could not take advantage of a nervy Arsenal start, with goalkeeper David Raya forced to make a sharp save from Igor Thiago.
Arsenal took the lead in the 61st minute through Madueke, who soared above Rico Henry and nodded Piero Hincapie's ball into the net.
Brentford levelled 10 minutes later when Michael Kayode's long throw was flicked to the back post where Lewis-Potter headed into the top corner.
The result lifted Arsenal to 57 points from 26 games, four ahead of Manchester City; at one point Arsenal were clear by nine points. But Arteta insisted his side will not change its approach.
“We have to do our job and we are going to have to come to all these places, the same as the rest of the teams, and we know how tough it is,” he told TNT Sports.
“You have to be at your best every game and have the luck that you need as well in games to conquer the three points each week.”
Arteta admitted he was praying Arsenal didn't fall to a late defeat.
Cristhian Mosquera stopped Thiago from scoring in stoppage time with a fine sliding tackle, before Brentford's top scorer then blazed over when clean through on Raya's goal.
Brentford were a constant threat from both corners and long throws, and Arteta said: “We scored the goal and the game was under total control.
“But against them, that's not enough because they just need somebody making a foul that is unnecessary, a ball in the channel, they push you, the clearance is not good, a throw-in, and then you have to pray because they are exceptional at what they do.
“The chaos that is in, and around that ball is very, very difficult to defend. We said to the players: 'If you want to win here, you're going to have to defend the box with your life'. We didn't do that on one of the actions, but they deserve credit, too.”
