Sir Alex Ferguson bows out of football as arguably the greatest manager in the history of the game.
But even the legendary Scot made a few mistakes during his 26-year spell at Manchester United.
Here are four players he should not have sold.
Not many footballers leave Old Trafford and still remain so fond in the hearts of Manchester United fans. Cristiano Ronaldo was different in that respect, he was an instant fan favourite the minute he arrived at Old Trafford - everyone knew he was something special.
However in 2008 Ronaldo shocked world football by declaring his desire to join his ‘dream’ club Real Madrid. Sir Alex Ferguson could do little to persuade the Portuguese star from leaving but managed to get one last season out of him and squeeze £80m from Real Madrid.
Ronaldo has gone on to become arguably the best player in the world and rightly so, scoring 146 goals in 135 appearances for the Los Blancos. Manchester United have invested in some decent signings with the money they received (i.e. Shinji Kagawa, David De Gea), but it’s unlikely the club will see a player with the same natural talent as the Portuguese star.
He could win games on his own, dazzle defenders with his array of skills and rifle shots into the back of the net.
Jaap Stam’s Old Trafford career was cut short in controversial circumstances after making critical comments about his team-mates in his autobiography. After a verbal brawl at a petrol station, Ferguson quickly told Jaap Stam that he was to be transferred and a deal was struck with Serie A side Lazio thought to be worth around £16.4m.
The Dutchman later expressed his anger of being transferred to Lazio without his consent, blaming a total lack of decency on the clubs’ part. Ferguson later accepted that perhaps selling Jaap Stam was the biggest mistake of his career.
Stam was a defensive rock for Manchester United, during his short spell at the club he won three Premier League titles and was an influential figure in the treble-winning season in 1999.
His beast-like persona and great aerial abilities made him one of Manchester United’s greatest defenders. His departure left a gaping hole in the team’s defence and it led to people wondering how much of a mistake it was letting the Dutchman go.
Paul Pogba: the Frenchman that left bitter tastes in the mouths of Manchester United fans last summer. The 19-year-old was on the verge of a breakthrough at Old Trafford and was supposed to be part of the clubs next generation of youth graduates - Ravel Morrison and Ezeki Fryers making up the rest of the list. Funnily enough, none of the trio actually made it to United’s first team.
In Pogba’s situation, a lack of first-team opportunities and lack of belief from Ferguson led to a falling out between the two parties. As the 20-year-old's contract was expiring the club decided to cut their losses and let Pogba join Serie A champions, Juventus. He soon proved his former boss wrong, starting 27 Serie A games for Juventus, scoring five goals and becoming an integral member of the squad.
The jury is still out on the 19-year-old but he shows huge potential and signs of former Frenchmen and Arsenal midfielder Patrick Vieira.
Pogba was the answer to United's midfield woes, but a lack patience and desire to play preserved him of that status. It begs the question: would fans still be crying out for a box-to-box midfielder like Kevin Strootman if Pogba was still at Manchester United?
Another product from Barcelona’s famous La Masia academy, Gerard Pique made a shock move to Manchester United in 2004. High expectations came with his signature but he failed to live up to those expectations, only making 23 appearances during his four-year spell at Old Trafford.
Now at 26-years-old, the Spaniard is a commanding presence in the back-line with credit to his strength and ability to read the game. Pique had been so impressive he was dubbed "Piquenbauer" by a Catalan newspaper last season when attracting flattering comparisons with legendary German sweeper Franz Beckenbauer.
The Spaniard was unable to force his way into Ferguson's first-team plans at Old Trafford and was sold back to the Catalan giants in 2008, where he has since earned the accolade as one of Europe's premier centre-backs.
Ferguson isn’t to be blamed for selling Pique. The Spaniard never got to grips with the physicality and pace of the Premier League, struggling to cement his place in Manchester United’s first team. However, since his move back to Barcelona, fans must now be thinking what could've been had he persevered through his troubles at the club.
Other honourable mentions: Ruud van Nistelrooy, David Beckham and Park Ji Sung.
Write for GiveMeSport! Sign-up to the GMS Writing Academy here: http://bit.ly/12evFlH
DISCLAIMER: This article has been written by a member of the GiveMeSport Writing Academy and does not represent the views of GiveMeSport.com or SportsNewMedia. The views and opinions expressed are solely that of the author credited at the top of this article. GiveMeSport.com and SportsNewMedia do not take any responsibility for the content of its contributors.