Jurgen Klopp says Sadio Mane's injury stopped Liverpool's 3-1 win over Everton on Saturday from being "perfect."
Mane went down following a duel with Everton left-back Leighton Baines midway through the second half at Anfield and had to be replaced by Divock Origi.
The Liverpool manager said he could not identify the nature of Mane's problem but that it appears unlikely that he will be fit for Wednesday night's meeting with Bournemouth.
"Today we played a really good game. Nearly everything was perfect, we win it, the performance was good [but] then we lose Sadio Mane," Klopp told a news conference.
"When I saw him in the dressing room, it didn't look like he'll be ready for Wednesday.
"We will see. Hopefully it's not that serious, but of course it's not nothing and that makes our life not easier, I would say.
"I don't want to speculate now. Obviously he has pain and it didn't look like it's only a knock or a muscle or something, but we have to wait.
"When I came in I was looking for him immediately and I saw him on the bed. He'd already had treatment, and it didn't look like he felt really comfortable."
Mane's importance to the team was underlined as he scored an individual goal to break the deadlock in the 228th Merseyside derby with eight minutes on the clock.
Liverpool moved nine points clear of their local rivals in the Premier League thanks to further goals from Origi and Philippe Coutinho.
Klopp said the victory was "deserved" and praised his players for the performance they delivered after an international break.
Liverpool now turn their attention toward midweek action as they welcome Eddie Howe's Bournemouth side to Anfield.
"I thought it was deserved," he added. "Like always, you have to learn a little bit from the game. We knew about the intensity we needed to be ready for, and I thought we were.
"After the first few minutes we controlled the game, we found the spaces between their lines, we brought Phil [Coutinho] into really good positions.
"I said to the boys before the game that it needs to be a mixture of being really smart and emotional -- not only emotional. I thought they did really well, controlled it and scored fantastic goals.
"The next game, Wednesday, we will be ready. It will be hard. You saw the last 20 minutes; for both teams it was like this. Having one day training to bring 10 different countries where the players come from after international duty, 10 different ideas, 10 different jobs to do and you have exactly 35 minutes -- the same for all of us -- to bring it to kind of one idea again.
"They did really well, but now we have to recover of course and then we need to be ready again.
"We will fight for everything. I thought the players showed again that they are ready to fight for everything. Hopefully we can stay in this optimistic mood and can get there."