Opinion: If Liverpool can't sign van Dijk, which other centre-backs should be under consideration?
Virgil van Dijk rising above the Liverpool defence for a header during a recent encounter between Southampton and the Reds.

Liverpool's raid on top-flight rivals Southampton was set to continue this summer as Jürgen Klopp was prepared to splash the cash on a new centre-back, with the Saints' Virgil van Dijk his key target in the propitious transfer window.

However, that move from Hampshire to Merseyside looks doubtful now that the Dutchman's current employers filed a complaint to the Premier League against the Reds' conduct in swooping for the player's signature.

There is no doubt that the title-challenging hopefuls need to reinforce their back line ahead of the 2017-18 campaign so a centre-half is in demand for Klopp.

But it remains to be seen whether the German dives into another English club's assets or searches for strengthening abroad, with Napoli's Kalidou Koulibaly one such named alternative.

Here are just a few candidates who haven't been linked but could come under consideration by Liverpool this summer.

Kurt Zouma

The 22-year-old Frenchman really has found life at Stamford Bridge difficult after completing a £12 million move to the capital three-and-a-half years ago.

Zouma was plagued with a long injury lay-off not too long ago after suffering a ligament rupture in his knee. Unfortunately for him he was sidelined for the next nine months.

Zouma did eventually return to action last October but his limited opportunities would become a frustrating attribute in determining his future at Chelsea as Antonio Conte's men were impressively flowing to the Premier League title, understandably keeping the centre-back out of the starting eleven.

In comparison to previous target van Dijk, Zouma is known for his similar physicality and pivotal pace, often case in a modern-day central defender, which is fairly replica of the Dutch international. Zouma would be a suitable replacement on Klopp's transfer target list.

The only stumbling block over this transfer becoming a reality is the reluctance of Chelsea to sell a promising figure in their first-team, despite Zouma being unquestionably adamant for regular minutes in the new season, though they might be tempted by a fair fee.

Matija Nastasić

Formerly of Manchester City, Nastasić has been earning himself rave reviews so far in the two campaigns he has spent in the German top division with FC Schalke.

Despite only featuring in 13 outings in his last 12 months at City, the Serbian talisman was a prospective talent in the ranks after winning the rights to be applauded from dedicated supporters; being a proud winner of the club's Player of the Month award in November 2012.

His consistent displays in the senior squad led the fans to voting him to be Young Player of the Season at the climax of the 2012-13 campaign, though he eventually fell out of favour at the Etihad Stadium.

Since transferring to the German city of Gelsenkirchen in 2015, Nastasić has gone from strength-to-strength and is using his experience of the pace and physicality of the Premier League as a beneficial advantage in the Bundesliga.

Without dispute, even for the young age of 24 years old, the centre-back is showcasing class composure in a such an intense environment.

Due to currently loving life in Germany, it seems unlikely that Nastasić would consider a return to England, but Klopp definitely takes care of his players.

Possibly the most similar outfielder to van Dijk in continental Europe, Nastasić, is what the Merseyside giants are looking for in this hectic summer transfer window.

Thomas Vermaelen

​Possibly the forgotten man in Catalonia, ex-Arsenal favourite Vermaelen has regularly been an outcast at the Nou Camp for Spanish dominance FC Barcelona.

The likes of Gerard Pique, former Red Javier Mascherano and pacey Frenchman Samuel Umtiti would all seem to be ahead of the Belgian in the club's pecking order.

A certain starter in the Gunners' top-flight sides, Vermaelen was forced to be circumvented at his lack of guaranteed play time last year and subsequently spent the 2016-17 campaign on loan at Italian outfit AS Roma - even his appearances were limited to a measly nine.

Whilst he isn't the stand-out centre-back that Liverpool supporters will be hoping for this summer, the 31-year-old would contribute his vital experience to this upcoming, talented Klopp team who mostly remain young.

His 110 outings for Arsenal will be well-remembered during his five-year stint in north London, and that knowledge of the division is possibly what the Reds were absent of in previous seasons after constant criticism in their back-four. Plus, he would likely cost just a fraction of what van Dijk would.