Arsenal manager Arsene Wenger has confirmed that goalkeeper Petr Cech will not feature in today's game against Tottenham Hotspur.
The 33-year-old suffered a hamstring injury in stoppage time against Swansea City and is expected to be out of action for at least three weeks.
Defender Laurent Koscielny will also miss the North London derby with midfielder Jack Wilshere expected to return next month after the international break.
"Petr Cech is out and Laurent Koscielny is not back," Wenger said.
"We have to check this morning that everybody who played on Wednesday is a available tomorrow.
"It is a calf injury [for Petr Cech]. He had a little groin problem but he declared himself 100 per cent fit. Then you have to trust the player. He's 33 years old and he knows his body. If he says he's fit then he is available.
"[Laurent] Koscielny is out. He has a small injury but he is out tomorrow and Tuesday next week. It's a grade one, so it's a very short period. I don't think he'll be available on Tuesday but next Saturday he should be alright.
"[Jack Wilshere is] not [running] yet. He is going to plan. He is doing well but we think three to four weeks. Maybe he will be available [after the international break]
"He is an important player in the plans of Roy Hodgson. We know that because I spoke with Roy about Jack. We need to do everything to make him available for us."