Arsene Wenger says Alexandre Lacazette will miss Saturday's visit of Manchester United with a groin injury.
The French striker scored his seventh goal of the season after three minutes of Arsenal's 5-0 thrashing of Huddersfield on Wednesday, before being substituted.
The 26-year-old was replaced by Olivier Giroud at half-time with Arsenal leading by Lacazette's early goal.
The Gunners probed for a second, and after Giroud (68, 87) scored his first, the floodgates opened, with Alexis Sanchez (69) and Mesut Ozil (72) also on target.
After the game, while Wenger praised his side, he admitted the Gunners "played with a bit of fear at one-nil".
He told the club's official website: "Lacazette has a groin problem and will certainly be out for Saturday’s game."
Wenger added: "I felt that I was not pleased with everything, but we started well and I think after that we slowly lot a bit of our edge, the urgency in our game and a little bit as well in the second half we gave them one or two chances.
"We missed as well the second goal, but after that, once we scored we played with freedom, with drive, with creativity and our link play became fantastic to watch in the last 20 minutes.
"I’m convinced that we played with a bit of fear at one-nil at some stage because we didn’t play with the freedom, the passes didn’t come early enough.
"We played a bit inhibited and when we scored the second goal everybody was suddenly had more movement and passed the ball quicker, they struggled as well maybe and thought that was game over.
"Maybe we benefited as well from the fact that they had to give a lot for 70 minutes and they collapsed a little bit in the last 20."