Arguably, the club has still not recovered from the legendary manager's exit, and while Erik ten Hag begins his summer transfer plans to get the Red Devils back to the top, we're remembering the superstar transfers that could have been during Fergie's reign.
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One of those was Brazilian legend Ronaldinho, who Manchester United were just days away from signing in 2004.
The iconic trickster, who was at Paris Saint-Germain at the time, was one of many the club tried to lure to Old Trafford during Sir Alex Ferguson's time as manager.
"He was away on pre-season and we were as close as announcing him and giving him a number but I think he ended up changing his mind at the last minute and signing for Barcelona," former midfielder Paul Scholes recalled to the BBC, remembering the star quality Eric Cantona brought to the squad when he joined in 1992.
"Then, three days later, we're playing against him and all trying to kick him because he didn't sign for us.
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"It was disappointing but I was lucky enough to play with some great players and he'd have just been another unbelievable player I'd had played with, but it just never happened."
Despite that setback, Ferguson got plenty of things right during his long, record-breaking reign as manager - as his still unbeaten record of 13 Premier League titles, two Champions League crowns, five FA Cups, four League Cups, a European Cup Winners' Cup, a European Super Cup, an Intercontinental Cup and a FIFA Club World Cup shows.
But although Ferguson turned United into a trophy-winning machine with his tactics and faultless formula for success, but even his legendary standing could not always entice the very best around to play for him.
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A decade on from his Old Trafford exit, talkSPORT.com looks at those near misses during Ferguson's 26-year tenure.
Goalkeeper - Petr Cech
Before becoming a legend at Chelsea, Cech could have become a Manchester United player.
At just 19, the Czech Republic international was making waves at Rennes and Sir Alex went on a scouting mission.
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But the goalkeeper missed out on a move because he was too young at the time.
"I went to see Petr Cech when he was at Rennes," he said in 2011. "He was 19 at the time and I said to myself, 'He's too young'."
Right-back - Philipp Lahm
Former Bayern Munich assistant coach Hermann Gerland revealed how the Scot tried to bring the versatile Lahm to Old Trafford early in his career.
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Able to play in either full-back position and in central midfield, the Germany legend was as close to being a complete footballer as possible.
Gerland coached the youngster at Bayern B and arranged for him to go on loan to Stuttgart.
"It was not easy to arrange. But at Stuttgart, Philipp could play in the Champions League. After three months he was the best player on the field against Manchester United," said Gerland. "Sir Alex Ferguson wanted him in England, I think that says enough."
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Centre-back - Vincent Kompany
The last Manchester City signing before the influx of Arabic money, Kompany went on to be one of the most important players in the Citizens' history.
But back in 2004, the Anderlecht starlet was one of Sir Alex's transfer targets.
The Scot's transfer target list from the summer of 2004 (when Kompany was just 18) revealed how the Belgian was being considered for a move.
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But a move never materialised and after joining Hamburg in 2006, he went to City two years later.
The rest is history.
Centre-back - Paolo Maldini
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Sir Alex Ferguson once tried to sign Paolo Maldini from AC Milan but was told to in no uncertain terms to 'forget it'.
Maldini's father, Cesare, told the United boss there was no chance of signing his son.
At an event in Italty, Ferguson said: "Well I did try. But when I met his father he was quite formidable. I got a shake of the head. That's all I got.
"He did say 'my grandfather was Milan, my father's Milan, I'm Milan and my son is Milan. Forget it'."
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Left-back - Bixente Lizarazu
Before Roberto Carlos established himself as the world's best left-back Bixente Lizarazu was the man.
But Bayern Munich rejected a move for the World Cup and Champions League winner out of hand.
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"I had the chance, I think in about 2001 or 2002, to go to Manchester United, but it stopped very quickly as Bayern said no," he told FourFourTwo.
"Alex Ferguson was keen to sign me and United had talks with Bayern, but Bayern said there was no question that I'd be leaving and so I was staying with them. I was very happy in Munich, but Manchester United did try."
Central midfield - Paul Gascoigne
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It was 1987 and Man United, a year into Sir Alex Ferguson's reign as manager, were playing relegation-threatened Newcastle in the First Division.
In midfield for Man United were Norman Whiteside, Bryan Robson and Remi Moses, 'all great footballers,' Fergie told David Frost in an interview.
"And he just tore them apart." He was talking about Newcastle's 20-year-old rising star Paul Gascoigne. English football was already alert to the talent this irrepressible player possessed and Ferguson knew he had to get him. But he failed to deliver.
"Off I go, and I'm lying by the pool when there is a Tannoy for me to take a call," Fergie explained. "It was [chairman Martin Edwards] telling me Tottenham had [signed him instead] by buying Paul's mum and dad a house in the north east."
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Central midfield - Zinedine Zidane
Had it not been for Ferguson's loyalty to Eric Cantona, the Premier League may have got to witness Zidane in his magisterial brilliance. But, as Martin Edwards revealed in his autobiography, the Scot knew he also had a temperamental talent on his hands.
"When Zidane was at Bordeaux, Les Kershaw, the chief scout, was telling me we should be interested in him and I mentioned it to Alex," he said.
"Alex said that Eric [Cantona] had also mentioned Zidane to him but Alex felt Zidane played in the same position as Eric.
"Having gone over to France to persuade Eric to re-sign for us, after the Crystal Palace incident [when Cantona was banned for eight months after clashing with a football fan at Selhurst Park in 1995], he felt that, if he had brought Zidane in, it may have affected Eric's position, so he stuck with Eric."
Right Wing - Arjen Robben
Despite his slight frame and tendency to play act, Arjen Robben was one of the most consistently feared wingers in Europe for the best part of a decade.
At Chelsea, Real Madrid and then Bayern Munich, Robben made the lives of full-back's a living hell. But he could have been a Red Devil.
Speaking to FourFourTwo he revealed: "I had a very good conversation with [Ferguson] over dinner in Manchester and we spoke about football and life. I also went and had a good look around the training ground and everything was good.
"But after I went back to PSV nothing happened. There was no real contact and the deal didn't happen. PSV were also negotiating with Chelsea at that time, so maybe they offered PSV more money? I don't really know.
"I spoke to Chelsea and I liked their plans. We had one meeting and everything was done pretty quickly. Had Manchester United offered me a deal straight after I met them, I would have signed there, but it didn't happen and I've got no regrets."
Left Wing - Ronaldinho
As Scholes explained, Ronaldinho came agonisingly close to signing in 2003, but the former Ballon d'Or winner instead moved to Barcelona.
Aged just 23, the Paris Saint-Germain and Brazil forward had won the World Cup the previous summer and was well on the way to becoming one of the best players in the world and current United midfielder Bruno Fernandes idolised him as an aspiring footballer.
In an interview with Four Four Two in 2015, Ronaldinho appeared to back up what Scholes said.
"It was a matter of 48 hours, but Sandro Rosell had told me way before I got the offer: 'If I become Barca president, will you come?'
"I said yes. It was only a matter of details with United when Rosell called to say he was going to win the election there. And I had promised to him that I'd play for Barca."
Attacking Midfield - David Silva
Like Kompany, Silva could have become a legend for the red half of Manchester, before ending up as a blue.
But the Scot was unwilling to change his tactics for the diminutive Spaniard.
"We watched Silva a lot when he was at Valencia," Ferguson is quoted by the Mirror as telling Sirius XM. "And the other player they had, the same type, years before it, played in that No. 10 role.
"My problem with that was you have to be very, very good to play in that position, because there's no defensive duties for them.
"So if you're wanting to be really successful, everyone has to do their turn, has to work, you know?
"So I had a difficulty with that. But, in the end, of course, there's the greats. You could say Lionel Messi was a No. 10 type, [Diego] Maradona, some fantastic players, and I don't dispute that.
"But at United we always found it difficult. The kind of No. 10 I used came from my experience as a footballer."
Striker - Alan Shearer
In his autobiography, Edwards also revealed Newcastle United and England legend Alan Shearer rejected Manchester United while at Blackburn Rovers.
The record Premier League goal scorer could have moved to Old Trafford, but chose not to out of loyalty to former Blackburn owner Jack Walker
"Shearer had been to Alex Ferguson's house, spoke to him and assured him he wanted to come," Edwards wrote. "The problem, I think, was with the chairman of Blackburn, Jack Walker, who was not a great fan of Manchester United, (we were) local rivals, both Lancashire clubs.
"He did not want Alan Shearer to come to Manchester United.
"Shearer was quite close to Walker, who was like a father figure to him, and I don't think Alan wanted to upset him by coming to United.
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