Liverpool are concerned Marko Grujic may have suffered a setback to from a long-term tendon injury, with the midfielder having missed a number of recent training sessions.
As a result, the 20-year-old has been left out of the travelling squad to face Plymouth Argyle in an FA Cup third round replay on Wednesday night.
Grujic had spent just short of two months out injured with a hamstring tendon issue and hasn't featured since the Reds' 2-0 win over Championship side Leeds United in an EFL Cup quarter-final on November 29.
But the Serbian youth international was progressing well from his knock and appeared close to a first-team return.
Liverpool manager Jürgen Klopp said of Grujic on January 6: "Yes [he is still injured], but he is on a good way too. Maybe the end of this week or the start of next week he will be back in team training.
"It was difficult and we had to do not too much because it was how it is with muscles, they all heal differently. In this case, he obviously took a little bit longer. He is not injured anymore, but he is not match fit."
Grujic did indeed return to training but, having missed a number of sessions recently, wasn't considered fit enough to face Plymouth at Home Park and will remain in Liverpool as the club assess his fitness.
It is the latest setback for Grujic, who has only made two starts since moving to Merseyside in the summer, and has yet to earn regular minutes for the club.
Grujic hopeful of making progress next season
The highly-rated midfielder, who signed from Red Star Belgrade in a £5.1 million move in January 2016 before staying on loan in Serbia to win the title with his boyhood club, will therefore be bitterly disappointed to miss out on the trip to Plymouth.
But he will hope his teammates can do the job and secure a fourth round clash with Wolverhampton Wanderers later this month, with Premier League fixtures unlikely to offer Grujic much football until the end of the season.
He has also made just one appearance for the Under-23s due to injury, meaning he could drop into the reserves for an extended spell as he looks to get back to full fitness.
The youngster recently declared his second season in England would be the one in which he asserts himself and he will hope to prove as such, having yet to demonstrate his obvious talent following an immensely promising pre-season campaign that saw him score three goals, including one in a 4-0 rout of Barcelona at Wembley Stadium.