Jurgen Klopp has omitted midfielder Naby Keita from Liverpool's Champions League squad, prompting concerns over the Guinean's injury.
Keita suffered a muscle during pre-season but there were numerous reports suggesting his issue was not significant - he was back on the bench for Liverpool's second game of the season before returning to the treatment table - but he is yet to play a minute of Premier League action.
Concerns over the severity of his injury have been sparked by Klopp's decision to leave Keita out of his European squad alongside fellow midfielder Alex Oxlade-Chamberlain, who is out with a hamstring injury that the boss has previously described as serious.
Liverpool will get their Champions League campaign underway against Napoli on Wednesday and will play all their group games, including meetings with Ajax and Rangers, before the World Cup later this year.
Keita is now not eligible for any of those fixtures and cannot be registered in the squad until January.
In Klopp's squad in place of Keita and Oxlade-Chamberlain are new signing Arthur, who joined on loan from Juventus on Deadline Day, and academy centre-back Stefan Bajcetic, who has been part of every Premier League matchday squad this season.
Bajcetic has split his time between the senior side and the academy, playing in defensive midfield for the latter.
Source : 90min