Mikel Arteta said Bukayo Saka was unable to finish Sunday's north London derby, raising doubts about the winger's fitness ahead of a huge week.
The England winger was replaced by Ethan Nwaneri four minutes from time as Arsenal beat Tottenham 1-0 in an entertaining but scrappy north London derby, settled by Gabriel Magalhaes.
Arsenal begin their campaign in the revamped Champions League against Europa League winners Atalanta on Thursday before visiting title rivals Manchester City on Sunday.
Asked for an update on Saka, Arteta said: "I don’t know. I made two changes with the front players and suddenly he’s down. I looked at the bench and the options that we had and we had to adapt. I don’t know exactly what it is but he could not continue."
Arsenal were without suspended midfield Declan Rice and six senior players to injury, including Martin Odegaard, with Nwaneri was one of five teenagers on the bench.
Arteta says his side's selection problems only made his players more hungry for the game as he talked up their "thick skin" following an important three points.
"Super happy obviously," the Spaniard said. "We know what it means to our club and our people to win a North London derby. We have the power to make them very happy so hopefully we achieved that.
"On the performance we had good moments and others where we had to suffer.
"We suffered because we had to adapt the plan because of the players that we had available. I loved it.
"The second we started to get that news, the team got hungrier and hungrier to play that game. It’s a big compliment to everybody at the club to behave in a certain way. It’s a tough week coming and instead of finding any excuses we did the opposite. We faced the challenge, played with courage and acknowledged the qualities we had to win the game.
"We have people that are hard and have thick skin. They love the game and we love winning. In order to love the game and win you have to do things that people call ugly. Enjoying those ugly things is a big compliment to this team right now. When you’re able to do that normally you get a good gift."
