Liverpool boss Jurgen Klopp admits Alex Oxlade-Chamberlain's injury is a concern suffered in victory against Crystal Palace in Singapore.
The No.15 was forced off with the issue during the latter stages of the first half in the win over Patrick Vieira's side in Singapore.
Offering an update post-match, Klopp told a press conference: "Of course it's very disappointing for us because Oxlade trained all the time really well since the pre-season started.
"It happened obviously with Ox in the past when it gets more intense and something can happen. Now this is just a muscle thing and that's OK. We had worse situations, so I'm OK with it.
"I don't know exactly how long it will take but he will be back and then it's all fine. He is obviously a top-class player and he can help us."
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