The 20-year-old has been ruled out of the crunch Anfield clash after suffering an ankle injury during Tuesday’s Champions League tie with Napoli, with fears growing that he could miss the bulk of the Reds’ festive fixtures.
That could hardly have come at a worse time for Jurgen Klopp, who saw centre-back Joel Matip ruled out for up to six weeks after fracturing his collarbone in the final seconds of Tuesday’s game. Another defender, Joe Gomez, is out for around the same period after fracturing his leg against Burnley earlier this month.
It means Klopp has just two fit, senior centre-backs to choose from at a crucial time of the season, with Dejan Lovren set to partner Virgil van Dijk against United.
Alexander-Arnold’s absence provides a fresh dilemma. The youngster was pictured on Thursday with his foot in a protective boot as he attended an EA Sports promotional event, and looks set to miss at least the Reds’ next two games, if not longer.
Klopp used James Milner in Alexander-Arnold’s right-back position at Bournemouth last week, but admitted afterwards that the midfielder would “probably have preferred every other position on the pitch”.
Nathaniel Clyne would be an obvious option to step in, but has been struggling with an injury of his own in recent weeks and has not started a Premier League game since May.
Nineteen-year-old Rafa Camacho played as a full-back for the first team during pre-season, and has impressed for the Reds’ under-23 and under-19 sides this term.
Fabinho, meanwhile, played as a right-back regularly for Monaco, his former club, and could be an emergency option – though the Brazilian has been growing into a midfield role and would surely not benefit from a switch.
United have issues of their own, with Luke Shaw, Marcos Rojo, Chris Smalling, Diego Dalot, Matteo Darmian, Scott McTominay and Anthony Martial all struggling ahead of this weekend’s game. Victor Lindelof and Alexis Sanchez are ruled out already.
Both Klopp and Jose Mourinho are scheduled to hold press conferences on Friday during which they will discuss their team selection issues.