Liverpool defenders Ibrahima Konate and Joe Gomez were both absent from open training ahead of their final Champions League group match at home to Qarabag.
It means head coach Arne Slot will go into a game they need to win to guarantee progress directly to the last 16 and avoid the play-off round with just one recognised senior centre-back in Virgil van Dijk.
Konate, who has missed the last two matches, was given compassionate leave following the death of his father last week, while Gomez was forced off with a hip injury in Saturday's defeat at Bournemouth following a collision with his own goalkeeper Alisson Becker.
The only other recognised first-team centre-back Giovanni Leoni was ruled out for the season with an ACL injury sustained on his debut in September.
Midfielder Wataru Endo replaced Gomez on the south coast while left-back Andy Robertson, over whom the club pulled out of talks with Tottenham at the weekend about a January move as he is out of contract in the summer, has also featured there.
Ryan Gravenberch has played the position before but his key role in central midfield is likely to rule him out, although midfield is one area where Slot has plenty of options.
Speaking ahead of the game, the Liverpool boss insisted his side can still win a trophy this season but accepted if they continue to under-perform at both ends of the pitch the growing criticism would increase significantly.
The Dutchman said securing silverware - they are still in the FA Cup and can guarantee qualification for the last 16 of the Champions League at home to Qarabag - would make it an "acceptable" campaign.
But it is their Premier League form which is attracting the scrutiny as Saturday's defeat at Bournemouth was their seventh of the season. It dropped them to sixth in the table and although they are only two points behind fourth-placed Manchester United, it prompted questions about their ability to qualify for the Champions League.
Former defender Jamie Carragher claimed the squad was not equipped to compete in the Premier League despite having £450million (€518m) spent on it in the summer, adding to the criticism coming Slot's way.
"I think it's going to be really difficult to quiet the outside noise with the position we are in in the league so even if we win a few games, every loss or every disappointing result will start the noise coming back again," Slot said.
"It's impossible to shut down the noise at a club like this if you are not competing for the league.
"Coming back on what is acceptable for me, I can say if we improve in both boxes, I think we are able to win something this season. If we only improve in one box, it is going to be really difficult to win something this season.
"If we can't improve in both boxes, it's going to be a lot of noise throughout the whole season."
Slot won the Premier League in his first year, Liverpool's second in five years having gone 30 years without a title, but has found the going tough second time around.
Watch Liverpool v Qarabag in the Champions League on Wednesday from 7pm on RTÉ2 and RTÉ Player. Follow a live blog on the RTÉ News App and on rte.ie/sport.
