Liverpool have completed a loan deal for Schalke's Turkey central defender Ozan Kabak.
The 20-year-old joins the Reds until the end of the season, with the club also having signed Preston North End's Ben Davies for £2m.
Defender Davies, 25, has signed a "long-term" deal at Anfield.
Marseille's Duje Caleta-Car was also a potential target, with the Reds exploring a number of options in defence because of injuries.
Liverpool have an option to buy Kabak for £18m - with add-on clauses - at the end of the season, but do not need to activate it until June.
For now, they will pay a £1m loan fee now with the potential for an extra £500,000 based on games played and how they fare in the Champions League.
The Reds are missing experienced centre-backs, with Joel Matip out for the rest of the season and Virgil van Dijk and Joe Gomez out with long-term injuries, while midfielder Fabinho, who has been standing in at the back, is also out.
Manager Jurgen Klopp named his 12th different centre-half partnership in 21 Premier League games for Sunday's 3-1 win at West Ham, with midfielder Jordan Henderson alongside Nathaniel Phillips.
On the arrival of Davies from Championship side Preston, Klopp said: "It's probably clear that in a normal transfer window, without any issues, we would not look at Preston [to see] if there's a player for us or something like that.
"Since our situation got clearer and clearer - the problems we had - when we saw him we got really excited about it and thought: 'Wow.'
"We see the quality and we see the potential as well because he's 25 and there's a lot to come for him."
Liverpool sign 'astonishing' Kabak
Kabak was recommended by former Huddersfield Town manager David Wagner, who coached him at Schalke and worked with Liverpool boss Klopp at fellow Bundesliga side Borussia Dortmund.
Before joining Schalke, Kabak played for Stuttgart and won the German top flight's Rookie of the Year award for the 2018-19 season despite the club being relegated.
Stuttgart's sporting director Thomas Hitzlsperger, the former Aston Villa midfielder, said it was "incredible how worldy-wise he is for his age".
"It's astonishing," Hitzlsperger added. "I see him every day and am amazed at how he mature he is."
Kabak, whose idol is Van Dijk, has played 14 times for Schalke this season, although the club are bottom of the table with the worst defensive record in the league.
Liverpool were linked with the Turk last summer after the departure of Dejan Lovren.
German football expert Constantin Eckner
After Kabak arrived in the Bundesliga in 2019, he quickly became one of the most promising centre-back talents in the league.
Sadly for him, he was not always able to show his full potential, as he was relegated with Stuttgart before joining a dysfunctional Schalke side.
Still, Kabak impressed many with his defensive skill set. He has been called the "Turkish Wall" because of his abilities in duels both on the ground and in the air.
His ball-playing talents have not been tested that much because Schalke often avoided any kind of constructive build-up. Kabak looks like a competent passer but he might need some time to adapt to Liverpool's possession-based system.
While he is a tremendous talent, Kabak gained a reputation in Germany for having a hot temperament.
He was suspended for four games earlier this season for spitting in the direction of Werder Bremen left-back Ludwig Augustinsson.
Given that he is only 20, he will still be growing a lot as a player and as a personality. And so, despite the hype, coaches, team-mates and fans will have to show patience with him.
Davies join Reds from Preston
The signing of Davies was completed following a medical on Monday.
The left-sided defender, who Celtic were convinced they had secured on a pre-contract agreement, came through Preston's youth system and has had spells on loan with York, Southport and Newport.
Burnley were also interested but it is understood Preston were not keen to sell to a local rival.
Bournemouth were considering a bid as part of a double deal also including Ben Pearson, while Sheffield United were also in the mix - but Davies jumped at the chance to move to the Premier League champions.
"It's a huge opportunity," said Davies. "Obviously it came as a bit of a surprise at first but once you start to get your head around it, the opportunity that is in front of me is incredible.
"I'd be silly to not make the most of it and learn from the players at the club."
The Reds have paid £500,000 up front with add-ons worth up to £1.1m relating to first-team appearances and any other achievements he contributes to, as well as any England honours he may win.
There is a 20% sell-on clause for Preston if Liverpool make any profit on a future deal for Davies.
Liverpool's 19-year-old Dutch defender Sepp van den Berg has joined Preston on loan as part of the deal.
Who is Davies? 'A real steady Eddie'
Former Preston and Liverpool defender Mark Lawrenson
Ben Davies has done well at Preston and has let his contract run down so he was going to move on in the summer. I didn't really see him as being good enough to be on Liverpool's radar.
He's a real steady Eddie. He's left-footed and quick enough but he's not got phenomenal pace or anything like that.
He's been good in the Championship, very good.
But I've watched him and thought, up against the extra nous and quality you get in the Premier League, on top of extra pace, it will be a test for him. You wouldn't want to just throw him in to face Manchester City next Sunday, put it that way.
This is obviously a great move for him, I just can't see him getting near the first team. Phillips has done well when he's come in and he is probably a better player.
So, Davies would be behind him and also Rhys Williams, so even before Joel Matip comes back and the other two long-term injured players - Van Dijk and Gomez - he is going to be below them on the list. And Fabinho and Jordan Henderson too.
I am not sure he will play very much, but the experience alone should be fabulous. I hope he experiences playing in the first team, but even if he is just sitting on the bench then it is still great for him.
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