Liverpool have already raided Southampton twice this summer, with the signings of Rickie Lambert and Adam Lallana. But the Saints are holding firm the third time around, not wanting to give up centre-back Dejan Lovren, who they consider their most valuable remaining player.

Liverpool, however, are understandably be in the market for an upgrade in defence, having seen just how porous their current setup is. But Lovren may prove to be out of reach, with Southampton said to want £25 million for the Croatian international.

Lallana’s signing is evidence that the club are willing to back Brendan Rodgers this summer. So with the need for a new first-choice centre-back ahead of next season, here are six alternatives to Dejan Lovren.

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Click on Hector Moreno to start the gallery

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Toby Alderweireld

Toby Alderweireld may be pushing for a move away from Atletico Madrid this summer after failing to get regular games last season.

He was thought to be an excellent purchase by Diego Simeone last summer, but the Atletico coach remained reluctant to rotate his squad over the course of the season. Alderweireld has been at the World Cup with Belgium, though playing mostly from the right-back position.

He was regularly able to show his class while playing in the Netherlands with Ajax and drew plenty of attention from the Premier League. After a disappointing season from a personal point of view, Liverpool may be able to offer Alderweireld an exit route and the chance of regular football in his favoured position.

Steven Caulker

It was a surprise when Tottenham opted to sell Steven Caulker to Cardiff last summer, as the young centre-back had shown a lot of promise in the season prior.

He’s young, strong and technically able, with plenty of time to further improve. Brendan Rodgers has a good recent history of bringing the best out of young players, and amid all the defenders linked with a move to Liverpool, Caulker may be the cheapest option, while also having the potential to be considered a complete success in the near future.

Jan Vertonghen

Jan Vertonghen is another Belgian international who has spent much of the past season playing out of position. The Tottenham centre-back saw most of his games at left-back, and while he’s able to play there to good effect, also doing so for his national side, his preference is understandably to play at centre-back.

There was talk earlier in the year that Vertonghen would move on from Spurs this summer with a view to joining to a Champions League club. Liverpool would be the perfect destination, with the team desperately in need of a player who can carry the ball out from the defence and initiate attacks.

He’d come at a high price, such is his value to Spurs, but there may be a chance at landing the Belgian if Vertonghen expresses a desire to leave.

Hector Moreno

Hector Moreno proved to be one of the stars of the World Cup before picking up a serious injury when out of the tournament to Holland. Moreno has been one of La Liga’s best centre-backs over the past few years, remaining consistent in a struggling Espanyol side, attracting attention from some of the bigger clubs in the league.

But this World Cup should act as the springboard for the Mexican international’s career. He’s already won a league title with AZ Alkmaar, but he’s more than capable of being a success in one of Europe’s top leagues for a major club. If the price is right, there will be few better options for Liverpool than Moreno this summer.

Inigo Martinez

Inigo Martinez may be in need of a move away from Real Sociedad. The centre-back was once thought of as one of La Liga’s brightest prospects, but hasn’t managed to properly fulfil that promise with the Basque side.

Brendan Rodgers knows what it takes to get the best out of precious talents, especially those whose careers have stalled somewhat. Inigo is technically gifted and has a fearlessness about him when defending in and around his own penalty area. He simply needs a talented coach and a good environment to get the very best out of him.

An under-the-radar signing for sure, but Inigo would be a great addition at Anfield this summer.

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Diego Godin

Atletico Madrid will do all they can to keep a hold of Diego Godin, with the centre-back sure to be interesting clubs throughout Europe after the season he’s had.

Godin is rightly considered one of the best and most underrated centre-backs in Europe, having been vital to so many Atletico victories over the past 12 months. He’s also managed to perform for Uruguay at the World Cup, despite disappointments and setbacks on and off the pitch.

At 28, Godin would be an ideal addition at Anfield and a notable step up in quality over the team’s current centre-back options.