Jurgen Klopp has admitted he is unsure when Alexis Mac Allister will return to action, revealing he has never seen an injury like the Liverpool midfielder has suffered.

Mac Allister was cut on his knee against Sheffield United last week, initially playing on with it bandaged up before he was forced off before the hour mark at Bramall Lane.

The 24-year-old missed the win over Crystal Palace and will not be involved for Liverpool's final Europa League group-stage match against Union Saint-Gilloise, a dead-rubber with the Reds already through as group winners.

While at first it did not appear to be a serious issue, the Liverpool boss gave a more downbeat update on Wednesday in his pre-match press conference.

"It's a bit more tricky than we thought at the first moment," Klopp said.

"The other boy stepped on his knee and the stud went through pretty much the muscle on to the bone. Now, we have to wait until the bone is healed and until Macca can deal with the pain, because it is pretty painful.

"Macca is actually a super-tough guy so we have probably to make sure just from an infection point of view nothing happens. That's really important."

Liverpool have taken a young squad to Belgium for Thursday night's match, with Mohamed Salah, Virgil van Dijk and Trent Alexander-Arnold among those left at home.

However, while those stars can be expected to return on Sunday when Liverpool host Manchester United in the Premier League, Klopp confirmed that Mac Allister will not be involved at Anfield.

"I never had this injury for one of my players before but now we have it," the Liverpool boss continued.

"I hope it will not take that long, I would like to say it's day by day - but that would look like he could maybe play the next game but he will not be ready for that as well.

"I hope the next three or four days he makes big steps and then we will see."