What was Manchester United's biggest transfer window mistake?

Manchester United splashed out over £150m in the summer transfer window - but what was their biggest mistake?

It's been quite the summer for Manchester United. Louis van Gaal was appointed as the replacement for David Moyes, and the squad needed a huge overhaul after finishing down in seventh place - unknown territory during the Sir Alex Ferguson era, with the Red Devils not even having European football to play this season.

Whilst over £150m has been pumped into squad reinforcements, United's spending took a while to get going. Only Southampton left back Luke Shaw and Athletic Bilbao midfielder Ander Herrera arrived before United met Swansea City on the opening day off the Premier League season, but the 2-1 defeat to Garry Monk's side sparked United into life.

Sporting Lisbon defender Marcos Rojo arrived for £16m after impressing at the World Cup with Argentina, and his international team mate Angel Di Maria arrived as the club's marquee signing in a £60m deal from Real Madrid. Come deadline day, van Gaal reunited with Ajax's Daley Blind after the pair fared so well in Brazil this summer, and that £14m capture was followed up with the stunning loan signing of Monaco striker Radamel Falcao.

These are all exciting signings, but United look massively unbalanced, with millions invested in their attack and little attention paid to their porous defence. Chris Smalling, Jonny Evans and Phil Jones have all looked shaky in the new three-man back line under van Gaal, whilst Tyler Blackett shouldn't be relied upon heavily at the age of just 20.

It's bewildering that United didn't spent money on improving their defence, and whilst it's easy to say that top defenders are rarely on the market, there was one staring United in the face - only for United to ignore him.

Morocan international Mehdi Benatia had been linked with United for some time having turned in a stunning season with Roma, with the 27-year-old establishing himself as one of the top centre backs in European football. However, interest turned Benatia's head, and after just one year in the Italian capital, he was looking to leave Roma.

United looked to be front runners after neighbours Manchester City ruled themselves out of the race, and whilst there was speculation after the Swansea game that Benatia would be arriving at Old Trafford, United missed out massively as the former Udinese man made a cut-price £24m move to Bayern Munich.

That's a reasonable fee for a world class centre back, but United chose to spend on their attack - which wasn't their issue. In the coming months, this will go down as United's biggest transfer window blunder - unless Smalling, Evans or Jones improve.

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