The Japan international has been injury-prone in his Gunners career and he suffered another setback earlier last week.

When asked in yesterday's press conference, Arteta was surprised by the injury blow for the former Bologna defender.

He added that the 25-year-old has remained in London as a precaution and will be assessed to find out the extent of the injury.

He said: "It is unbelievable, because the kid works so hard. He had an incident in training this week."

"We don't know yet the extent of that [knee] injury but as a precaution we kept him [in England]. We'll see what happens."

Arsenal will face Bournemouth in a pre-season friendly tomorrow. Jurrien Timber looks the likely candidate to feature at left-back.

Jakub Kiwior and Oleksandr Zinchenko have also travelled with the team and they could be involved off the bench if required.

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