Mikel Arteta will be out for the rest of the month with a calf strain, Arsenal boss Arsene Wenger has confirmed.
Arteta was injured in training ahead of Sunday's defeat to Manchester City and forced to miss his first Premier League game of the season.
A scan will determine the full extent of the problem, but Wenger does not expect Arteta back before the transfer window shuts.
The manager said: "He has a scan on Monday. He will be out for approximately three weeks. It is a calf strain."
Wenger confirmed he is seeking reinforcements as a matter of urgency as he prepares for a spell of five games in 17 days.
He said: "We are in the market. We try very hard (to strengthen)."