Arsenal boss Arsene Wenger has revealed the reason why Theo Walcott was a late withdrawal from Sunday's Premier League clash with Stoke City.

The England winger sustained an abdominal muscle strain which forced him out of the line-up, being replaced by German youngster Serge Gnabry, with Wenger admitting it is a bit of an unknown problem.

"He had an abdominal muscle problem," said Wenger.

"Is it a question of days? I hope so. He had a little problem before the Marseille game (on Wednesday) and it became a bit worse.

"It is a bit mysterious because we don't really know what it is."

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