Scotland captain Andy Robertson sustained a shoulder injury during his nation's 2-0 defeat to Spain last week, and there are fears he could now be out for at least a month as he returns to Liverpool.
The implications of this for Jurgen Klopp are concerning, as the Scotsman has started every Premier League game for his team so far this season.
This Saturday's Merseyside Derby represents an opportunity for another member of the Liverpool squad to step up and ease their manager's concerns, but who might the German pick to fill his shoes against Everton?
Kostas Tsimikas
The most obvious option at Klopp's disposal would be a like-for-like replacement in Kostas Tsimikas.
In many people's eyes this would be a no-brainer, but despite remaining a popular figure at Anfield, the 'Greek Scouser' has consistently flattered to deceive since scoring the winning penalty against Chelsea in the 2022 FA Cup Final.
Tsimikas does, however, come in to the match off the back of a relatively strong showing in the international break. He provided an assist in a clean sheet away victory over the Republic of Ireland, before his Greece side came close to another clean sheet against the Netherlands, losing 1-0 courtesy of an injury time penalty converted by club teammate Virgil van Dijk.
The added concern over selecting Tsimikas this weekend comes from the opposite flank. The Greek is inarguably more of an attacking-focussed full back, but with Trent Alexander-Arnold likely to start at right back, Klopp's new-look system relies on his left back having a bit more defensive responsibility in order to free up Alexander-Arnold's creativity.
This is not to say that Robertson has had no licence to drift forward for Liverpool this season, but with Trent in the side he has at times sat back to almost create a three-at-the-back system in possession.
This is not a role that perfectly suits Tsimikas' style, particularly when considering that Tsimikas' defending was suspect for Leicester City's goal at Anfield only last month.
Nevertheless, Tsimikas remains a viable option, particularly if Klopp should opt to revert back to a system more similar to that of seasons past.
Joe Gomez
Joe Gomez represents another option to plug the the gap in Liverpool's defence.
The Englishman has played in this position for the Reds before, albeit sparingly, and predominantly many years ago.
A shortcoming of Gomez in this position would be the fact that he is right-footed, and not especially strong on his left.
This is unlikely to be a major issue with the defensive aspect of the role, which would be his more important responsibility, but as Luis Diaz - who also prefers his right foot - will be the probable starter on the left wing, the left flank will be limited in terms of overlaps and crossing opportunities.
Selecting Gomez in this position would be an experiment, but it could also be an experiment that makes sense.
As discussed, Liverpool have a tendency to establish a back three with their left back and centre halves upon the many occasions when Trent roams forward.
This aspect of the role is something Gomez would be able to adopt instinctively, as a natural centre half.
Gomez has played well enough when called upon so far this season. He might not be the same player that combined with Virgil van Dijk to create one of the most formidable defensive partnerships in the world before his knee injury, but he is nevertheless a useful squad player at Anfield.
He is experienced in big games, and this might be the tipping point in Klopp's selection process.
Jarell Quansah
Jarell Quansah is an option for very similar reasons to Gomez stylistically.
Naturally, the youngster lacks the experience of Gomez, so it would be a big ask to bring him into an unfamiliar position in such a big match, but Klopp has shown this sort of faith in him on numerous occasions already, and has largely been rewarded for it.
Quansah was given an opportunity to come on against Newcastle United in difficult circumstances earlier this season and nobody will forget the comeback that ensued with him on the pitch.
He was solid throughout the cameo, and truthfully he has been every time he's been called upon. His form this season earned him his England Under-21 debut in the recent international break.
It is not beyond the realms of possibility that Klopp will show further faith in the young centre back; he has in the past shown a tendency to use young players as injury replacements, regardless of the opposition.
Stefan Bajcetic, for example, started against Real Madrid last season despite his inexperience, and who could forget Tyler Morton’s performance at the San Siro?
Klopp appears to be of the reasonable opinion that the experience matches such as these provide to a young player can be invaluable in their development, and with Gomez struggling to replicate the heights that he reached a few years ago, Liverpool's staff might well feel that investing in Quansah's future will stand them in better stead in the long term.
Ultimately, the decision will come down to Klopp's mentality going into the game.
At a glance, a home match against a side that has consistently battled relegation in recent years seems like it should be comfortable, and thus it might be wise to adopt an attacking focus in starting Tsimikas.
Having said that, derby matches do tend to forego factors such as these, plus Everton have been performing better than results have suggested so far this season - with the Blues sitting only a place behind their local rivals in the Premier League expected points table (sitting sixth and seventh respectively).
Furthermore, Everton went into the international break off the back of a convincing 3-0 win over Bournemouth, in which Jack Harrison - the man likely to directly face off against Liverpool's left back - got both a goal and an assist, so there is reason for Klopp to be wary of how defensively capable whoever lines up at left back this weekend is.
Whether we see Tsimikas, Gomez or Quansah lining up at left back for Liverpool this Saturday lunchtime will tell you a lot about how Klopp views his Merseyside rivals.
Tsimikas' inclusion would show belief that his side can get at Everton, Gomez's would portray the most wariness of Everton's attacking threat, and Quansah's would fall somewhere between the two.
