Arsenal manager Arsene Wenger has admitted that he is unsure of how long Theo Walcott will be absent with his "mysterious" stomach injury.

The England international winger was a late withdrawal from the Gunners' starting lineup that beat Stoke City 3-1 on Sunday after complaining of abdominal pain.

Wenger has revealed that Walcott was also suffering prior to Arsenal's Champions League win over Marseille on Wednesday, but has confessed that he does not have a diagnosis of the 24-year-old's condition.

"We hope we haven't lost Walcott for a long time. He has a muscular abdominal problem but I don't know how serious it is," Wenger told BBC Sport.

"Is it a question of days? I hope so. He had a little problem before the Marseille game and it became a bit worse. It is a bit mysterious because we don't really know what it is."

Walcott was forced to spend three weeks on the sidelines after being struck down by a similar problem when he was on international duty with the Three Lions earlier this year.