Joel Matip could be unavailable until February 10 as a result of Liverpool's ongoing dispute with Cameroon over the defender's international availability.
Matip featured for the Indomitable Lions at the World Cup in 2014 but has since refused call-ups to his national team, effectively retiring from international duty.
Cameroon, however, argue that the 25-year-old should be available to play, meaning Liverpool would risk punishment by FIFA if they were to field him while he could be playing for his country at the Africa Cup of Nations.
"We can confirm that Liverpool FC contacted FIFA about the matter and our services answered by directing the club to the applicable provisions," a FIFA spokesperson told the Liverpool Echo.
"A player who has been called up by his association for one of its representative teams is, unless otherwise agreed by the relevant association, not entitled to play for the club with which he is registered during the period for which he has been released or should have been released pursuant to the provisions of this annexe, plus an additional period of five days."
The Echo reports that this has infuriated Liverpool, who - along with Matip - are said to have given up attempting to reach an agreement with the Cameroon Football Federation and believe no regulations have been breached.
If that is the case and FIFA refuse to step in, Matip could be ruled out until February 10 if Cameroon reach the Cup of Nations final five days earlier.
That would see the centre-back miss their FA Cup third-round replay against Plymouth Argyle and Premier League matches against Swansea City, Southampton, Chelsea and Hull City.
The lack of clarity forced Matip to sit out of Liverpool's clash against Manchester United at Old Trafford on Sunday, with the Reds drawing 1-1 against their rivals.