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.
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