Liverpool star Naby Keita was taken to hospital immediately after his side's 1-0 defeat against Napoli on Wednesday night, with the Guinean rumoured to have suffered a back injury.
The Reds' official website has revealed that the former RB Leipzig midfielder, who was stretchered off in Naples during the first half, is yet to be discharged from hospital, while reports including from journalist Melissa Reddy suggest the player has 'severe back pain'.
He is now a major doubt for Sunday's crunch clash against Manchester City.
During the first half of the Reds' 1-0 defeat on Wednesday night, Keita fell to the turf with no other player within ten yards of him, before being stretchered off and taken to hospital.
The club said in a statement: "Keita was transferred to a local hospital with the club doctor, where - with the midfielder's agreement - he underwent a number of precautionary health checks to assess his condition."
In his post match interview, Reds' boss Jurgen Klopp admitted that he was unsure of what exactly was wrong with the 23-year-old, whilst also taking the blame for the lacklustre performance.
Speaking to Sky Sports, the German said: "It is his back, that's what I heard. I don't know exactly. We have to wait.
On his side's disappointing late defeat Klopp took responsibility.
He said: "A big part of that performance was my fault for sure but I need at least one night to watch it again and see what was the fault but it was not like it should have looked.
"I am pretty sure the reasons will be obvious and then we will sort that but we were not good enough and normally if you are not good enough you lose games.
"When you have the ball you have to play much calmer."
Liverpool are set to depart Naples on Thursday morning, although no decision has been made yet on when Keita will be discharged from hospital.