The Cameroonian has joined long-term absentees Virgil Van Dijk and Joe Gomez on the sidelines after ankle ligament damage sustained in last week's win at Tottenham was deemed serious enough for him not to play again this campaign.
With midfielder Fabinho, who has filled in at the back for most of the season, not expected to return from a minor muscle problem until this weekend's Manchester City match it was no surprise manager Jurgen Klopp had a last-minute visit to the transfer market.
While both will take some time to get up to speed, Klopp can at least be reassured he now has the numbers to cover what has been a problem position this season.
Here the PA news agency takes a look at the issues facing Liverpool's established names – and the potential solutions.
Matip has been plagued by injuries during his time at Anfield, struggling to string together a run of appearances, but the ankle ligament problem sustained at Tottenham last week was the final straw for his season.
Virgil Van Dijk
Klopp admits the chances of Van Dijk, out since October with an ACL injury, returning this season are not impossible but they have to "hope for a miracle". The Holland captain has been a huge absence both for his defensive capabilities and his leadership qualities.
Gomez had surgery in November on a knee tendon injury sustained on England duty and Klopp admits there is no chance of him returning before May.
The Brazil midfielder has slotted into centre-back in place of Van Dijk seamlessly but a minor muscle problem will keep him out until the weekend's visit of Manchester City.
Liverpool's captain became the second midfielder pressed into action at centre-back because of injuries. The England international has played four Premier League matches in defence, conceding three goals, and is likely to continue there in the immediate short term at least.
Teenager Williams, 19, had done well as a temporary stop-gap and featured in all six Champions League group stage fixtures. He was unfairly singled out for criticism for a mistake in the FA Cup defeat to Manchester United, considering a year ago he was on loan at Kidderminster Harriers, but the arrival of two new defenders will allow him more time to develop.
Phillips gained experience playing on loan for Bundesliga 2 club Stuttgart last season and has made only six appearances for Liverpool. He had his best game for the club alongside Henderson in the win at West Ham and will likely start at home to Brighton on Wednesday.
The 20-year-old Turkey international was on Liverpool's radar last summer when they allowed Dejan Lovren to leave but the £40million price quoted caused them to think again. Kabak arrives with a glowing reference from former Schalke coach and Klopp's best friend David Wagner, but will have to settle quickly and do well enough for Liverpool to take up the £18million option to buy.
A surprise signing from Preston which even Klopp admitted would not have happened had their injury crisis not been so bad. At an initial £500,000, plus £1.1m of add-ons, there is little risk in the deal for Liverpool who will be able to make a profit on the player should he not make the step up from the Sky Bet Championship.