It's no secret that Manchester United are on the hunt for a new centre-back this summer following the bosman departures of Nemanja Vidic and Rio Ferdinand, with Louis van Gaal planning a 3-4-1-2 formation for next season.

Their priority target is Borussia Dortmund's Mats Hummels, who played an integral part in Germany's successful World Cup campaign.

The 25 year-old, famed for his defensive ruggedness, aerial ability and fluency on the ball - often drawing parallels with Franz Beckenbauer - is widely regarded as one of the leading centre-backs in world football, but the Red Devils' pursuit of him hasn't gone so swimmingly.

Many offers, ranging from £20million-£30million, have been regularly alleged in the tabloids, but Black-Yellows boss Jurgen Klopp appears determined not to sell.

With that in mind and only a month of the summer window remaining, the Premier League side need to think of some viable alternatives.

And being the ever-helpful bunch we are at Football Fancast, we've decided to list SEVEN of them...

Mats Hummels

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NEVEN SUBOTIC

Neven Subotic (2)

Borussia Dortmund's Mats Hummels may be off limits but Manchester United could find better luck pursuing sturdy centre-back partner Neven Subotic.

The 25 year-old, linked with a Old Trafford switch on numerous occasions in the past, is rated equally highly at Westfalen, but missed the majority of last season through injury whilst former understudy Sokratis excelled in his absence.

A dependable, more passive centre-back than Hummels, Subotic often doesn't get the credit he deserves. No doubt however, the Serbian international is one of Europe's top defenders - just take a look at him in action last term:

//www.youtube.com/embed/YV1uB16MEgQ?rel=0

Subotic's pace, tackling ability and composure in possession particularly stands out. And despite injuries last season, the 6 foot 4 defender still produced consistent form, as detailed below:

Subotic

That sideline bout however gives United a way in; Jurgen Klopp now has three high-quality centre-backs on his books and with just two years left on Subotic's contract, could be convinced to part with the Serbian.

THOMAS VERMAELEN

Vermaelen

Manchester United's plans to sign Thomas Vermaelen are well known, having been strongly linked with the Arsenal centre-back for the majority of the summer window:

The 28 year-old is regarded as one of the Premier League's leading defenders and currently dons the Gunners armband. But a mixture of injuries, poor form and the rise of centre-back partnership Per Mertesacker and Laurent Koscielney saw him make just seven league starts last season.

No doubt however, a run of regular football could easily see the Belgium international return to his former stature. He was named in the PFA Team of the Year for his debut Premier League season and van Gaal clearly feels he can unlock that level of performance once again. Here's a short clip of Vermaelen in action:

//www.youtube.com/embed/QTJyWnQbLkQ?rel=0

Like Hummels, he's combative in the air, composed in possession and often plays on the front foot. And United will feel their chances of signing the former Ajax man will have significantly improved, following news that he's rejected a contract extension at Arsenal:

FABIAN SCHAR

Fabian Schar

If it's Mats Hummels' ability on the ball that Louis van Gaal desires most, he need look no further for an alternative than FC Basel centre-back Fabian Schar.

Statistically, the Switzerland international was the best defender in the Champions League last season, as detailed below...

schar cl

And his World Cup performances weren't too bad either, making eight interceptions during two outings at Brazil 2014.

The 22 year-old has an interesting knack for scoring goals, even taking up spot kick duties for Bebbi...

//www.youtube.com/embed/MIe6I323HPc

And also netted this incredible strike as a youngster at FC Wil...

//www.youtube.com/embed/dH1mLudmGgg?autoplay=1&loop=1&playlist= dH1mLudmGgg

Quick, technically exceptional and also capable of playing at full-back, the 6 foot 2 defender would excel in a back three. He's been rated as lowly as €6.5million in the past but recent speculation suggests United will have to battle Arsenal and Tottenham for his signature:

EDER BALANTA

Balanta

Another young centre-back that's attracting interest from Europe's top clubs, including Liverpool, Barcelona and Juventus, is Colombia international Eder Balanta.

The 21 year-old has thoroughly impressed since his debut for River Plate in 2012, making 30 appearances since and muscling his way into Los Cafeteros' senior squad.

He's described on FIFA's website as "left-footed, powerfully built, strong in the air and a fearless tackler ... blessed with skill and speed." Here's a short clip of Balanta in action:

//www.youtube.com/embed/NApExJhZwEY

Impressive stuff indeed. Did I also mention that Balanta is an absolute monster on Football Manager?

But the Red Devils will have to act quickly, with news that Valencia are closing in on a €6.5million deal for the 6 foot centre-back:

BENEDIKT HOWEDES

Schalke centre-back Benedikt Howedes has been linked with a Premier League move for some time, and that could finally be realised this summer after an impressive World Cup campaign with Germany.

Indeed, despite being labelled as Die Mannschaft's weakest link at Brazil 2014, the 26 year-old produced strong form throughout, as detailed below:

Howedes

Here's some of his highlights from Germany's successful World Cup campaign:

//www.youtube.com/embed/DE4LYksdMEA?rel=0

Perhaps most importantly for the Red Devils, as well as offering significant leadership qualities, the Miners skipper can operate at right-back or left-back, making him an ideal defender for a back three and a useful squad member.

But it could take an unjustifiable offer to prize Howedes away from the Veltins-Arena, with Schalke issuing a hands-off warning last month:

FEDERICO FAZIO

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One cut-price Mats Hummels alternative said to be on the Old Trafford radar is Sevilla centre-back Federico Fazio:

Despite not making Albiceleste's World Cup squad, the Argentina international was in strong form last season to help Los Palanganos claim the Europa League title, as viewable below:

fazio

Fazio measures in at whopping 6 foot 5, making a formidable force in the air, but also offers quality in possession, being also capable of playing in defensive midfield.

Oh, and don't mess with him, or he'll punch you in the stomach:

Furthermore, according to TalkSport, the 27 year-old's release clause stands at an incredibly cheap €10million.

John Stones

Everton defender John Stones

John Stones' Premier League career may stand at just 21 appearances thus far, but the Everton defender is already tipped for an incredible future after making it onto England's reserve list for Brazil 2014.

Indeed, although the 20 year-old's defensive game still leaves something to be desired, he was absolutely incredible last term when bringing the ball out of defence, as viewable below:

//www.youtube.com/embed/ExtM3JTv630?rel=0

That quality on the ball appears to be what Louis van Gaal is looking for this summer and the former Barnsley prodigy possesses it in abundance. Notice his impeccable passing statistics from last season:

John Stones

But with suitors hardly in short supply, it would likely take a Luke-Shaw-sized fee to convince the Toffees to sell this summer: