#3 David Beckham
David Beckham, the midfield magician of Manchester United's legendary class of 92', caused a massive heartbreak for all fans when he decided to move to Real Madrid in 2003. It was a move that added to Manchester United's blushes as they lost out on a generational talent. Repeated feuds off-the-pitch with United's greatest manager, Sir Alex Ferguson, meant the player had no option but to leave.
Selling David Beckham will always be remembered as a mistake as he then went on to become a Spanish Champion with Real Madrid and played alongside the likes of Zidane, Ronaldo Nazario, and Luis Figo.
#2 Paul Pogba
In 2012, a young Paul Pogba left Manchester United to join Italian giants Juventus on a free transfer. Pogba established himself as one of the world's best midfielders during his time in Italy. He also went on to become a four-time Italian champion with Juventus. Manchester United would go on to regret allowing this move to take place only to purchase him again.
Hence, considering his immense commercial value and football qualities that he had developed in Italy. In 2016, Manchester United decided to make him the world's most expensive player and signed him again for £89.3 million.
A cost that United could have avoided had they not let go of him in the first place.
#1 Cristiano Ronaldo
Cristiano Ronaldo is a player who needs no introduction at all. He is probably the greatest player of all time to play the sport. At the same time, he is also one of the most beloved players to have ever donned a Manchester United jersey.
Ronaldo made headlines in 2009 when it was announced he would be making a move to Real Madrid in a transfer worth up to £80 million. It is no wonder that Manchester United came to regret this move as Cristiano Ronaldo went on to win five Ballon d'Ors, four Champions League titles, and two Spanish titles away.
However, the love for Cristiano Ronaldo never faded at Old Trafford. It was on deadline day of the last transfer window when Manchester United announced that Cristiano would be signing for the club for a second time.
It is no secret that Manchester United let go of Cristiano when his best years were ahead of him. Yet, with Cristiano back for a second spell, this move is sure to take away any regrets.