Van Gaal tests 3-4-1-2 again - how many centre backs does he need to sign?

Louis van Gaal has used his 3-4-2-1 system in both of Manchester United's pre-season games to date – sparking talk of him using it in the Premier League.

Van Gaal, 62, replaced David Moyes as United boss earlier this summer, and earned plenty of plaudits for leading the Netherlands to the semi-finals of the World Cup in Brazil. With a previously untried 3-4-1-2 system entering the tournament, van Gaal masterminded a stunning 5-1 demolition of 2010 champions Spain, before wins over Australia, Chile, Mexico and Costa Rica followed, only for Argentina to dump them out on penalties.

Now looking to improve on United's lowly seventh place finish last season, van Gaal has already implemented the same system having used it in pre-season friendlies against Los Angeles Galaxy and Roma, winning those games 7-0 and 3-2 respectively.

The system appears to suit certain players perfectly; particularly Luke Shaw at left wing back and Juan Mata in behind the strikers. Yet with only three senior centre backs on the books at the moment, the change in system could force van Gaal's hand in the transfer market.

Jonny Evans, Phil Jones and Chris Smalling have started together as a back three, but the depth behind them is thin. Youngsters Michael Keane and Tyler Blackett have been given playing time by van Gaal, but there is little indication as to whether those two will feature in the Premier League.

Van Gaal has regularly preached that he would have no hesitation in playing young players if they're good enough, but signing at least one - arguably two - centre backs is a must before the deadline. Arsenal's Thomas Vermaelen remains a top target for van Gaal, but the club still lack a dominant centre back of the ilk of Rio Ferdinand or Nemanja Vidic.

The likes of Mehdi Benatia (Roma), Eliaquim Mangala (Porto) and Mats Hummels (Borussia Dortmund) have all been strongly linked, and that's the kind of calibre of centre back United should be looking to land - even if Vermaelen does arrive.

Strength in depth is key to United's rebirth, and if van Gaal intends to use three centre backs - a position which they're already short in - means he must work hard to add players to resolve United's shaky defence.

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