Arsene Wenger says he is uncertain over how long Theo Walcott will be out for after the winger missed Arsenal's 3-1 win over Stoke on Sunday with a mysterious injury.
The England international was named in the starting line up for the game at the Emirates Stadium but was forced to pull out before kick-off, and Wenger says he is in the dark over extent of the injury and how long it will keep him sidelined for.
"He had an abdominal muscle problem, I don't really know what it is," he told Sky Sports.
"Nobody can tell me whether it is just a question of days.
"He had a test before the game and I decided to play him but he had a little problem before the Marseille game (last week) and it then became a bit worse.
"It's a bit mysterious, because we don't really know what it is."
Walcott is unlikely to feature for Arsenal in their Capital One Cup clash against West Brom on Wednesday, and could also be a doubt for their next Premier League fixture against Swansea.
The Gunners currently sit top of the Premier League following their win over Stoke, which came thanks to goals from Aaron Ramsey, Per Mertesacker and Bacary Sagna.
£42.5 million signing Mesut Ozil picked up three assists and the man of the match award, and Wenger says he is delighted with the German's contribution since his deadline day move.
"I didn’t expect to score so many headers from free-kicks against Stoke, but the delivery is very important and the deliveries were good today,” the Frenchman continued.
"Like the team he gave a lot on Wednesday night (against Marseille), but he showed his class today and he worked hard as well."