Arsenal fear Rob Holding will miss between three and four weeks with the hamstring injury that forced out of Saturday's game at Manchester City.
Centre-back Holding suffered hamstring tightness in the warm-up at the Etihad leading to him being replaced in Mikel Arteta's starting line-up by David Luiz.
Holding had a scan to assess the severity of the injury today and the diagnosis could see him see him miss Arsenal's next six fixtures leading into the next international break.
Holding has been a regular since the start of the season, being named in Arsenal's starting side in all but one of their eight games so far this campaign.
Thursday's Europa League trip to Rapid Vienna will be the first game Holding is sidelined for.
In the next three weeks Arsenal will also play further European games against Dundalk and Molde plus league matches against Leicester, Manchester United and Aston Villa before the next two-week break in early November.