Jurgen Klopp has said Dejan Lovren faces a "tight race" to be fit for the first leg of Liverpool's round-of-16 Champions League tie against Bayern Munich at Anfield next Tuesday.
Lovren's potential absence means Klopp could have a selection headache in central defence, with Virgil van Dijk suspended for the visit of the Bundesliga champions.
Neither Lovren nor Joe Gomez travelled to Spain for Liverpool's warm-weather training camp this week as they continue their recoveries.
"Dejan is not here and Joe is not here," Klopp told Liverpool's official website. "That's never a good sign, I would say, but we will try everything to make Dejan available for Munich. It will be a tight race.
"For him, it makes sense to be in another place to do what he has to do. It wouldn't have helped if he was here, so we will try everything -- that's clear."
Lovren has not featured since injuring his hamstring against Wolves in the FA Cup last month, while Gomez recently had further surgery to aid his recovery from a lower leg fracture.
Summer signing Fabinho, normally a defensive midfielder, could deputise in the heart of defence, having already played there against Wolves and Brighton.
Meanwhile, long-term absentees Alex Oxlade-Chamberlain and Rhian Brewster took part in a training session in Spain on Tuesday.
"The boys had to do a bit of core work, passing and the rondos and it's nice [that they could be involved]," Klopp said.
"This afternoon they will have to do their own stuff again, and hopefully we can integrate them step by step."