Liverpool's defensive problems continue to grow after Jurgen Klopp confirmed Fabinho suffered a hamstring injury in the 2-0 Champions League win over Midtjylland on Tuesday.
Brazil midfielder Fabinho – filling in at centre-back due to the absence of Virgil van Dijk and Joel Matip – pulled up while tracking back in the Group D fixture and went to ground shortly before being treated by Liverpool's medical staff.
He was replaced by youngster Rhys Williams in the 30th minute as Diogo Jota, whose effort brought up Liverpool's 10,000th goal in all competitions, and Mohamed Salah scored to secure a hard-fought win over the Danish side at Anfield.
Klopp is already without key player Van Dijk after the Netherlands star suffered a serious knee injury in the Merseyside derby against Everton earlier this month, and the Reds' boss is unsure over the severity of Fabinho's problem.
"Exactly the last thing we needed. I don't know, he felt his hamstring so that's not good," Klopp told BT Sport.
"He didn't feel it that much, he said he could've played on but not sprinting so that doesn't help. We will see, we will have to do a scan and see but clearly it's not good."
Klopp also withdrew captain Jordan Henderson at half-time, but revealed the switch was not related to injury.
"We had to make the change at half time with Hendo – he said he was fine but in these moments you have to be responsible and the plan before the game was to give him around 45 minutes so he would be okay for West Ham [on Saturday]."
It had been expected that Matip, who has not featured since the Merseyside derby, would be fit to return against West Ham, but Klopp could not make any assurances.
"I don't know, we have to see," he said in his post-match news conference.
"Look, if it would be only one game we play, if it was the last game of the season, I think we could make him fit for one game – but we play three days later again and we need players again."
Should youngster Williams be called upon against West Ham, he will at least go into the match on the back of a solid showing alongside Joe Gomez.
Williams made one tackle, one interception and gained possession three times during his 67 minutes on the pitch against Midtjylland, though the Hammers would be likely to provide a much tougher test.