The final decision to sell is said to have made by United boss Sir Alex Ferguson.
It certainly isn't the first time that Ferguson has sold one of United's prized assets, and here we remember five other top players that left Old Trafford.
How did it work out, and were the players sold at the right time?
DO YOU AGREE WITH OUR VERDICTS? HAVE YOUR SAY AT THE BOTTOM OF THIS ARTICLEPAUL INCEA top player for United and a vital cog in the machine of what many supporters still regard as the finest of the Ferguson years - the 1994 double winners.
The combative midfielder signed in 1989, won the FA Cup in his first season and the pots pretty much kept coming.
It was known however that Ince and Ferguson had a difficult and at times tempestuous relationship.
And the Scot's mood would hardly have improved when United lost both the league title on the last day of the season in 1995 and the FA Cup final to Everton (United were generally poor that day but Ince was nowhere to be seen).
Paul Ince left Manchester United for Inter in 1995
United fans weren't too happy that summer however, when Ferguson sold Ince to Inter for £7.5m - especially when his replacement was the inexperienced Nicky Butt.
But we all know what happened next - Fergie's marvellous youngsters stunned English football with a superb double.
Ince was half decent for Inter, and later Liverpool, but the wonderful benefit of hindsight has shown us that Ferguson got the best from Ince, and knew when to sell.
Verdict: United enjoyed the best years of Ince. The decision to sell him was brave, but time has proved correctANDREI KANCHELSKISA lovely player and again an important part of that thrilling Ferguson team that won the double in 1994.
In his four years with the club the Ukrainian delighted supporters with his exciting wing play and brilliant goals.
But Ferguson felt the time was right to sell Kanchelskis in the summer of 1995 (along with Ince and great United favourite Mark Hughes).
Supporters wondered quite what Fergie was up to as he sold the player to Everton for £5m, but he certainly had the last laugh.
United boss Sir Alex Ferguson sold Andrei Kanchelskis to Everton
Kanchelskis often impressed with Everton, particularly in his first season when 16 goals helped the Merseysiders to sixth place, but the pots were being won at the other end of the East Lancs Road.
After that first season at Goodison Park he never properly recaptured the form of his United years, and again it seems Ferguson got the best out of him.
Verdict: You have to say Sir Alex sold him at a pretty good time. United went on to dominate the game while the Ukrainian was never quite the same againDAVID BECKHAMThere was a lot of nonsense talked by some United supporters when David Beckham was sold.
Make no bones about it: Beckham was a magnificent player for United, one of the finest of the Ferguson years.
Breaking through as part of the team that 'couldn't win anything with kids' (copyright A Hansen esquire) he gave United eight memorabe years of first team action, with his and the club's finest hour coming with the 1999 treble. And he was still a superb influential player in 2003.
But the manager seemed to tire of the whole roadshow surrounding the player - the 'Beckham brand' if you will.
And when that famous boot accidentally caught Beckham in the boat race after United's FA Cup exit against Arsenal the writing was on the wall, and Ferguson sold the midfielder to Real Madrid for £25 million.
David Beckham left United for Spanish giants Real Madrid in 2003
In many ways Beckham is still going strong of course (who writes his scripts?) - he looks likely to travel to his fourth World Cup next summer for one thing and turns out for AC Milan when he fancies.
But for a man used to silver at Old Trafford, he only won one Spanish league title in a frustrating four years for Real Madrid.
Admittedly United went through a relatively lean period in those years, but still weighed in with a league title, FA Cup and League Cup. 3-1 to United then.
Verdict: Beckham ideally would have played for a couple more seasons at United, but the relationship between him and Ferguson had soured to such an extenct that that the decision to sell probably had to be takenJAAP STAMSir Alex admits to a mistake here, and tis true that United could have had a fair few seasons more of quality from the brilliant defender.
An extremely popular player with United supporters (I can still hear 'Jip Jaap Stam was a big Dutchman' in my head from that extraordinary week in and around Barcelona in 1999) and a towering presence in the defence that helped Ferguson to land his historic treble.
United won three successive league titles during Stam's time with the club, but you cross the gaffer at your peril and Stam's autobiography lit the touchpaper in a big way.
Stam claimed among other things that he was illegally tapped up before being brought from PSV Eindhoven and that the United manager had told his players to dive to win penalties.
Jaap Stam controversially joined Lazio from United in 2001
A furious Ferguson decided to sell the defender to Lazio for £16.5m in 2001 [folklore has it that Ferguson told Stam to enjoy his final match as it would be 'his last game playing for the club'].
Stam went on to play for six more years, with spells at AC Milan and Ajax after his time in Rome.
A few years back Ferguson admitted: 'At the time he had just come back from an Achilles injury and wethought he had just lost a little bit.
'We got the offer from Lazio,£16.5m for a centre-back who was 29. It was an offer I couldn't refuse.But in playing terms it was a mistake. He is still playing for Ajax ata really good level.'
Verdict: Sold too early. Could have played for United for maybe three or four more years
RUUD VAN NISTELROOYA player that seems to divide United supporters.
Nobody can doubt he was a prolific goalscorer, with 150 goals in 220 appearances (with his 38 in Europe a club record).
You could argue that he was slightly unfortunate to play during a time when United weren't completely dominating the game (there was Mr Abramovich arriving at Chelsea for one thing) but it has to be said United won one league title in five seasons with van Nistelrooy. I've done the math and that makes it 10 in 12 without him.
Things didn't seem to be right for one reason or another in 2006. Ferguson left him out of his starting line-up for United's League Cup final with Wigan. There were reports of a training ground bust-up with Cristiano Ronaldo.
Ruud van Nistelrooy was a prolific striker for Manchester United but Sir Alex decided the time was right to sell to Real Madrid in 2006
When Real Madrid came knocking that summer, Ferguson opened the door for the Dutchman to leave.
Van Nistelrooy has done well with the Spanish giants, and is a popular figure with their demanding public but just look at what you could have won Ruud.
United have been rampant and magnificent in the three years since the striker departed, with a hat-trick of league titles and a European Cup safely engraved on the roll of honour.
There would appear to be little doubt that his exit paved the way for Ferguson to reshape his team for the 2006-07 season, where United put a stop to what threatened to become a mini-era of success for Chelsea.
Verdict: Nobody can take away Van Nistelrooy's record, but a masterstroke to sell. United reshaped their formation in 2006 and haven't looked back since.