Arsene Wenger says Alexis Sanchez picked up a slight injury in the win over Manchester United.
The Chilean was instrumental in the victory over the Red Devils, scoring twice in the 3-0 win.
He was substituted with 10 minutes to go, with Wenger confirming post game that the attacker had tweaked his groin.
Wenger explained that he remained nervous because Sanchez is due to feature for Chile on international duty, and wants him to come back in top condition.
He said: "He has a little groin problem. Unfortunately he goes to Chile. You cannot stop him from going to Chile and he loves so much to play for his country and he will play against Brazil [on Friday] and Peru [next] Tuesday so the game at home against Brazil he will not want to miss. Hopefully he will come back in good shape."
Arsenal face Bayern Munich in the Champions League in the week after the international break, and the Gunners will need Sanchez fully healthy to stand a chance.
He added: "My plan is to pray now that everyone comes back from international games without any injury because we have a small group."
Sanchez is the type of player who, as Wenger suggests will play through the pain for his country, which could be to Arsenal's detriment.
He took a while to find form after a busy summer with Chile at the Copa America, and the last thing Arsenal need is for their star man to suffer a setback having hit such fine form at last.