Manager Jurgen Klopp revealed in his pre-match press conference that Trent Alexander-Arnold will miss the match because of a foot injury he suffered against Napoli in the UEFA Champions League on Tuesday, per the Liverpool Echo's James Pearce:
He joins Joel Matip and Joe Gomez among Liverpool's defensive absentees, giving Klopp a selection headache ahead of United's visit to Anfield.
With only two fit senior centre-backs, the German manager will likely have to pair Dejan Lovren with Virgil van Dijk on Sunday.
Meanwhile, James Milner is the obvious choice to deputise at right-back, as he did last time out in the league against Bournemouth.
Nathaniel Clyne is also available to step in, although he may not be able to play 90 minutes given he has been injured:
It is not an ideal time for Liverpool to be facing an injury crisis, with five Premier League games coming between now and Jan. 3.
The Reds' 4-0 victory over the Cherries saw them move into top spot in the English top flight, but they can afford no slip-ups, with Manchester City just a point behind them.
Liverpool are favourites to win Sunday's match against United, and deservedly so.
They have yet to lose a league game this season and have conceded just one league goal at Anfield since February.
Meanwhile, Jose Mourinho's Red Devils are struggling. They are sixth in the Premier League but followed up a decent 4-1 win against Fulham in their most recent domestic game with a dismal 2-1 defeat at Valencia on Wednesday:
However, Mourinho will likely relish the chance to inflict Liverpool's first defeat of the season.
And United's forward players will surely feel they can exploit Klopp's makeshift defence, even at Anfield.