Curtis Jones was not part of the Liverpool squad involved in the first training sessions in Dubai, with the midfielder instead working separately.
A total of 33 players flew out at the start of the week, with Darwin Nunez to follow, but the full squad are not in training at present.
His omission was unexplained, but it has now been revealed that the 21-year-old is not yet fully fit having suffered a new fitness problem.
When the Liverpool squad took to the training pitch on Wednesday, Jones instead joined rehabilitation fitness coach Dr David Rydings in light jogging around the perimeter.
While his team-mates wore boots, Jones was seen wearing trainers, with the midfielder as yet unable to join in contact training.
Jones’ setback is the latest in a long line of problems for the youngster in a difficult season so far, having missed 15 games before the break and only featuring seven times.
He sat out the final game before the World Cup with an unknown issue, which may have extended through the past three-and-a-half weeks to ensure he is not fully fit for the restart.
Days after that 3-1 win over Southampton, Liverpool announced that their No. 17 had signed a new contract, tying him to the club until 2027.
Liverpool squad pictured in training on Wednesday
Goalkeepers: Kelleher, Adrian, Davies, Mrozek
Defenders: Matip, Gomez, Phillips, Quansah, Robertson, Ramsay, Tsimikas, Chambers
Midfielders: Thiago, Elliott, Milner, Keita, Oxlade-Chamberlain, Bajcetic, Cain, Corness
Forwards: Salah, Diaz, Firmino, Carvalho, Clark, Doak, Frauendorf, Stewart