Liverpool midfielder Thiago Alcantara limped off during Saturday's 2-2 draw at Fulham with what appeared to be a hamstring injury.
The Spain international had been heavily involved, making 62 touches, before he needed to be withdrawn five minutes into the second half.
That substitution worked out well for Liverpool in the short term as replacement Darwin Nunez came off the bench to score and assist on his EPL debut.
But Liverpool manager Jurgen Klopp will be hoping to have Thiago back as soon as possible.
Klopp now has four sidelined midfielders. Alex Oxlade-Chamberlain also has a thigh problem, while Curtis Jones has a lower leg injury and Naby Keita has been ill.
Liverpool published a statement on the club's official website after the game.
It began: "Liverpool are waiting to discover the extent of the injury Thiago Alcantara suffered during Saturday's draw at Fulham."
Quoted in the statement, Klopp admitted that the situation was concerning but suggested that the solution was unlikely to be signing another player.
Klopp said: "I know what will now come up, it's clear. We said we don't need a midfielder because we have enough - and we actually have enough, but the problem now is we get punished for something that is not our responsibility really because things like this can happen.
"Nobody could imagine that Curtis gets the thing he gets; it is nothing serious but he is a young boy and it is a kind of stress reaction. Bodies are like this.
"Naby is only ill and he will now be back definitely next week again. Oxlade happened early and now with Thiago that is, of course, not good and we will see.
"Look, a transfer must make sense now and in the long-term; we have midfielders, we have still enough midfielders. It is not that we lack midfielders, but it's just some of them are injured.
"This is not a good situation, I don't like it at all, but we have to see how we react on that - but for sure not panicking."
Klopp had earlier told BT Sport that Liverpool had not been good enough at Craven Cottage.
He said: "We got a point from a really bad game."