Jamie Carragher fears Philippe Coutinho's injury could cost Liverpool in their challenge for a first Premier League title.
The Brazilian will have a scan on his ankle on Monday after he was hurt in Saturday's 2-0 win over Sunderland at Anfield, with Liverpool fearing he has suffered ligament damage.
Coutinho has contributed five goals and five assists in the league so far this season to help Liverpool climb to second in the table, one point behind leaders Chelsea.
Former Liverpool defender Carragher thinks a long absence for the 24-year-old will affect their title bid.
He told Sky Sports News HQ's new Premier League Daily programme: "It could be huge. He's Liverpool's best player.
"I think Liverpool's XI, playing week in week out, can match up to almost any team in the league [but] have they got the squad the other sides have got? I don't think so, to be honest.
"I go back to last season and the influence of Kevin De Bruyne at Manchester City. He got an injury at a similar sort of time and was out for a couple of months.
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"It was a massive blow for City and it really cost them in challenging for the league. City had a better squad last season than Liverpool probably have now.
"It is a worry going forward and it will affect them. The flip side is in the last few weeks you've had Joel Matip coming in and they're looking a lot tighter at the other end of the pitch.
"Maybe there may not be a need to score three or four goals at one end every game because they're looking a lot better defensively.
"It may not just be a case of someone coming in and taking Philippe Coutinho's place and getting goals and assists.
"It's making sure you're tighter at the other end and I think the addition looks like one of the outstanding signings of the season."
Divock Origi replaced Coutinho against Sunderland and later scored the opening goal, taking his tally for the season to three, and former Liverpool midfielder Jamie Redknapp thinks the Belgian could act as a long-term replacement.
He said: "It wouldn't surprise me if Jurgen Klopp were to go for Origi. He scored on Saturday and had a big impact on the game and I think he likes him.
"Daniel Sturridge has tremendous ability - we all know that - but the work ethic that Klopp wants from his team, I'm not sure he possesses that.
"You also can't learn what Daniel can do on the ball so it balances itself out. I like Daniel Sturridge and I think he's got amazing ability.
"But is he a Jurgen Klopp type of player? I'm not sure. Maybe then you can drop Firmino and he can drop to the left where Coutinho has been playing.
"Lallana's been in great form but he's had a little injury. He has got options so I'll be fascinated to see what he does.
"It depends if Sturridge is fit first of all but with Origi scoring at the weekend, he does give you another option."