Liverpool manager Jurgen Klopp says Dejan Lovren has a more serious muscle injury than before, adding he cannot put a time frame on the centre-back's recovery.
Lovren went off after 53 minutes of the 2-0 Champions League win away to Salzburg on Tuesday, having managed only 40 minutes of the 3-0 Premier League victory over Bournemouth last weekend.
The defender will miss Saturday's game against Watford at Anfield and Klopp admits he is unsure when the 30-year-old will be able to return.
"He is out, muscle this time – more serious than last time," Klopp told reporters on Friday. "We don't have a time frame."
With Joel Matip also sidelined with a knee injury, Klopp has only Virgil van Dijk and Joe Gomez as his senior centre-back options amid a gruelling run of fixtures.
After the Watford match, a team largely comprising youth and fringe players will face Aston Villa in the EFL Cup on Tuesday, with the rest of the squad in action in a Club World Cup semi-final 24 hours later.
With league games against second-place Leicester City and Wolves to come before the turn of the year, Klopp accepts his lack of defenders is a worry.
"It's a concern," he said. "It's not the first time we are in a situation like this: last year, one game Fabinho played at centre-half. Unfortunately, he is out as well. It's not too cool.
"At the moment we have two – we should take care of them, pack them in cotton wool and ask them what they want to do in training. Apart from that, we have to be creative; we have the kids, of course, with Ki-Jana [Hoever] and Sepp [van den Berg].
"We have defensive-minded midfielders, there are different systems where you can use different kind of defenders as well. That's how it is.
"At the moment, I have a lot of ideas, but I hope for most of them I never have to use them, to be honest."
- India men maintain third spot, women seventh in latest FIH rankings
- Turkey to end coach Kuntz’s contract after he criticised players -reports
- Indian sports news wrap, September 18
- Spurs family behind Richarlison, says skipper Son
- UEFA Champions League: Last ever group stage starts as Man City looks to defend title