#3 Failing to properly replace Peter Schmeichel till 2005
Manchester United have employed three of the best goalkeepers to have played in the Premier League in the form of Peter Schmeichel, Edwin van der Sar, and David de Gea.
However, there was a gap of five years between the departure of Schmeichel and the arrival of van der Sar, in which Manchester United tried various goalkeepers with little to no success. This list included Mark Bosnich, Massimo Taibi, Fabien Barthez, and Tim Howard.
Barthez was arguably the most successful of the lot, but none of them managed to replace Schmeichel. Ultimately, Manchester United signed Edwin van der Sar from Fulham for a fee of £3.5 million.
The Netherlands international proved to be an important addition to the Manchester United backline. He made 266 appearances in all competitions for the club, and won the Premier League four times and the Champions League once. He retired in 2011, paving the way for David de Gea.
#2 Selling Jaap Stam
Sir Alex Ferguson has admitted openly that selling Jaap Stam in 2001 was a mistake.
Stam joined Manchester United from PSV Eindhoven in 1998. The centre-back was a world-class player during his prime, with his pace, strength and consistent performances making him a fan favourite at Manchester United. He made 127 appearances in all competitions for the club, winning the Premier League three times and the Champions League once during his time there.
In 2001, Stam was sold to Lazio, with Manchester United signing experienced French centre-back Laurent Blanc as the replacement. His subsequent performances for Lazio and later AC Milan raised questions as to why he was sold, with Ferguson admitting that it had been a mistake to let him go.
The Netherlands international retired in 2007 after a stint with Ajax. He is now a football manager, having coached the likes of Reading, PEC Zwolle and Feyenoord. He is currently the manager of FC Cincinnati.
#1 Appointing David Moyes as his successor
The day Manchester United had been dreading arrived on May 19, 2013, when Sir Alex Ferguson managed his last Manchester United game. It was a thrilling 5-5 draw against West Bromwich Albion, and Ferguson retired in sensational style.
Manchester United had already announced the arrival of Everton boss David Moyes as Ferguson's replacement. Moyes had managed Everton for eleven years, and Ferguson had played a key role in his appointment as the manager of Manchester United.
However, things did not go according to plan. Moyes struggled with the Old Trafford outfit, and poor performances resulted in Manchester United sacking him in April 2014. The club later appointed big names like Louis van Gaal and Jose Mourinho, but results continued to oscillate during their reigns.
The Premier League giants are yet to reach the heights of the Sir Alex Ferguson era, although there have been signs of improvement under the current management of Ole Gunnar Solskjaer. Moyes is currently managing West Ham United, who have been one of the better teams in the league this season.
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