Arsène Wenger gave an update on Theo Walcott's recovery from injury at his press conference on Friday:

on Theo Walcott’s fitness…
Theo Walcott is planned to come back into my group on August 31, beginning of September latest. He’s doing well but he’s not completely ready. I would say end of August.

on his availability for England in September…
To play an international match, that could be a bit early.

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