Jack Wilshere will see an ankle specialist on Thursday to assess an injury he suffered during Arsenal's 2-1 Premier League defeat by Manchester United.
England midfielder Wilshere, 22, limped off after he was tackled by United defender Paddy McNair on Saturday.
Arsenal Manager Arsene Wenger said he did not know whether Wilshere would need an operation.
"The specialist will decide that," Wenger said.
Speaking after Arsenal's 2-0 Champions League victory over Borussia Dortmund, Wenger said: "Wilshere sees a specialist, then we'll know more."
Wenger had previously said he expected the midfielder to be out "for the next few games".
Arsenal travel to West Brom in the Premier League on Saturday.