Liverpool center-back Virgil van Dijk is to see a specialist to assess the extent of his hamstring injury.
The Netherlands defender, who has played in every Liverpool league game this season, was substituted at half-time in Monday’s defeat at Brentford.
There is no timescale on how long Van Dijk will be out for but the injury appears worse than originally thought.
The Reds’ other centre-back options are Joel Matip, Ibrahima Konate, Joe Gomez and Nathaniel Phillips.
Liverpool, who are sixth in the Premier League and seven points off the top four, face Wolverhampton Wanderers in the FA Cup third round on Saturday.
After the defeat by Brentford, Liverpool manager Jurgen Klopp said: “Virgil felt a little bit the muscle and said it is fine, and he is a very good judge of these kind of things. But I didn’t want to take any risks.
“The physios looked quite happy when I said we don’t take risks. It’s not an injury, he just felt the intensity.”
Liverpool have been hampered by numerous injuries this season, with forwards Luis Diaz and Diogo Jota both working their way back to fitness following significant issues.
Their next league games are away to Brighton & Hove Albion on 14 January and at home to Chelsea on 21 January.