Arsenal midfielder Aaron Ramsey was made to miss Saturday's North London derby after suffering a groin injury ahead of the match.
The Welshman recorded a hat-trick against Everton last weekend, helping the Gunners to a 5-1 win, but was unable to put in a performance against London rivals Tottenham Hotspur, who claimed a 1-0 home victory through a Harry Kane header at Wembley Stadium.
Ramsey was replaced by Mohamed Elneny in the starting lineup, and his presence was sorely missed, as the scoreline suggests.
"Ramsey is injured, he could not participate," Arsenal boss Arsene Wenger told reporters prior to the match.
"I have put one more midfielder in, we have an attacking team. We put one more defensive midfielder in.
"Jack [Wilshere] comes in, he was sick so I hope he’s back to his level, he has a good training week."
The loss leaves Arsenal six points adrift of the top four, in sixth place, and they could face a real fight to get back in the Champions League, having missed out last season.
Speaking after the match, Wenger blamed his players' missed opportunities for the defeat.
"Well I felt in the first half we missed three or four on the counter-attack and at that level it’s very difficult to swallow," he explained.
"Of course in the first half we had plenty of opportunities where you expect a better final ball for us.
"Once they scored we were wobbling and Spurs could’ve scored more but in last 10 minutes we should’ve come back to 1-1. ‘The first goal had a big part to play and unfortunately they scored with a header."