Arsenal were given an injury scare as defender Gabriel was carried off on a stretcher in their 3-2 pre-season victory over Manchester City.
It is too early for the Gunners to know the full extent of the problem but it could cause manager Arsene Wenger problems in central defence just a week ahead of the club's opening game of the new Premier League campaign.
Per Mertesacker is expected to be out until the New Year after he sustained a knee injury, while Laurent Koscielny will probably not be ready for the visit of Liverpool having not yet resumed full training following his exertions at this summer's European Championships with France.
"He's in pain. Let's hope that the pain is not a sign of bad news," Wenger said of Gabriel's injury on Arsenal's official Twitter account.
Sergio Aguero put City ahead in Gothenburg but goals from Alex Iwobi, Theo Walcott and Chuba Akpom turned the game on its head.
Kelechi Iheanacho reduced the deficit before a lengthy stoppage after the injury to Gabriel, who had to be carried from the field following a clash with Raheem Sterling.