Alex Oxlade-Chamberlain suffered a muscle injury during Liverpool's 2-0 victory against Crystal Palace on Friday that requires further assessment, Jürgen Klopp confirmed.
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."
Alisson Becker and Diogo Jota were forced to sit out the final match of the Reds' pre-season tour of Asia.
Asked whether the pair would be fit for the Community Shield with Manchester City on July 30, the boss replied: "Ali, I think, has the chance for City and Diogo not.
"Ali, he feels a muscle, abdominal. It's nothing serious but, again, we prepare a full season. So he can train but just not like before, so he should not play in the moment. Not normal goalie training but he has a pre-season, so he doesn't lose time.
"But yeah, these kind of things happen. The boys have to travel a lot and train and you never know exactly.
"It's only little things, nothing serious but we have to be careful because the rest of the season is much longer than the start."