Liverpool have spent the last few months without Andy Robertson, who required shoulder surgery after picking up an injury with Scotland. That left the Reds with one senior left-back - Kostas Tsimikas.
However, the Greek landed horribly on his own shoulder against Arsenal, breaking his collarbone and leaving him out of action indefinitely. Liverpool are now without a natural, senior left-back as they look to maintain their hold on the top of the Premier League.
So who can Jurgen Klopp actually call on? He has three actual options right now - with a couple of hypotheticals on top. Here's what he can do.
The best option
The most obvious option (and the one Klopp almost certainly goes with week-to-week) is Joe Gomez. The defender isn't a natural left-back as a right-footed centre-back but he's somehow versatile enough to pull it off.
Of course, Brendan Rodgers did use Gomez at left-back after he signed him in 2015, while he's also been a regular at right-back. We all saw against Arsenal that Gomez is very useful at left-back, too.
There are a couple of problems, though. Firstly, it's just asking a lot of Gomez to play there every week, especially with his injury history. Klopp almost certainly wants to find ways to rotate him.
The other issue is that Gomez is also Trent Alexander-Arnold's cover at right-back. That's a more important role than ever as the Scouser has been switching to midfield in games. He can't do that with no one to cover him at full-back.
So while Gomez is the best option, he can't be the only option.
The youth options
Luke Chambers has been a rotation option for Liverpool this season. Klopp has brought him into the Europa League setup, handing him 137 minutes so far.
He started the 5-1 win over Toulouse, for instance - a game that showed he can contribute to a winning senior team. Chambers also got the nod against Union SG. That was a difficult game with which to judge anyone, however, as Klopp rotated heavily.
But it all goes to show that Liverpool see Chambers as on the fringe of the senior team. Now the double injury brings him closer to the starters and don't be surprised to see him in a slightly bigger role this January.
Calum Scanlon is essentially the alternative to Chambers from the academy. He's played twice for the seniors this season - coming on for Chambers in the Europa League ties against Toulouse and Union SG.
That alone suggests that Klopp sees Chambers are slightly ahead of Scanlon but it's close. So close, in fact, that he may well get a chance to move ahead of his teammate next month.
We don't think Scanlon will start ahead of Chambers or Gomez but there could be a substitute appearance in there. Impress with that and who knows? Everything is wide open right now.
Harvey Elliott / Curtis Jones
High-energy, high-work rate and both are comfortable on the left. It's entirely possible that Liverpool trust one of their England Under 21 stars to do a job at left-back in a game where they'll control plenty of possession.
No one should outright expect this but as an alternative option - and if Klopp doesn't want to throw-in a kid - it remains a possibility.
Now, this one is hard to judge. Stefan Bajcetic can almost certainly play comfortably at left-back. He's got the engine, he's got the quality on the ball, and he's a natural defender. Liverpool have also used him on the left side of midfield.
But he also hasn't played. It's not clear when Bajcetic will be back but if it's anytime soon, Liverpool might just fancy easing him in at full-back rather than in a full-blown midfield role.
It seems highly unlikely that Liverpool would throw Jarell Quansah in at left-back. He's not a natural left-sided player and he's still learning in the Premier League. Quansah also isn't a natural attacker - he'd play the role in a very static, defensive way. That would necessitate a change of system for Liverpool.
But at the same time, the Reds lack options here and Quansah could well be seen as a 'safe' option at some point to avoid leaking goals down that side.