Jaap Stam
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Sir Alex Ferguson was no stranger to getting rid of big names throughout his time at Old Trafford, from Paul Ince and Steve Bruce to Roy Keane and David Beckham, but he famously regarded Jaap Stam as the one player he shipped out too soon.
Stam's time in Manchester was short compared to the majority of the players in this countdown, but the Netherlands international left an indelible mark on the club during his three-year stay.
The centre-back became the most expensive defender in history when United signed him for £10.6m in 1998, but that still proved to be a bargain as the club went on to win the Premier League title in each of his three full seasons in England.
Stam was also a major part of United's treble-winning season in 1999, being named the UEFA Club Best Defender of the Year for that term and the following campaign.
The Dutchman's standing in the game was also confirmed by the fact he was named in the Premier League PFA Team of the Year in each of his three seasons at United before controversially being sold to Lazio in 2001.
