It is probably the most daunting managerial job in world football: replacing Sir Alex Ferguson.
The short answer is that he will never be replaced. The 70-year-old will forever be immortalised at Old Trafford, and he even has a statue now outside its entrance...just in case you forget.
A poisoned chalice? An amazing opportunity?
One thing is for certain, United will not be short of applications once the great Scotsman decides enough is enough.
However, despite the high interest that will obviously be shown for the potentially vacant position, one would expect Sir Alex to have a huge say as to who his successor should be.
Here are five contenders for the coveted job.....
Roberto Martinez may not be in many people's minds when it comes to discussing the next United boss, but the Spaniard is a definite wild card who cannot be ruled out.
At just 39, Martinez is one of the brightest young managers in the game and has earned the respect of many for his achievements at both Swansea City and Wigan.
Senior figures in the game are very impressed and pleased that the Lactics boss has earned his stripes at lower levels, rather than walking straight into a glamour job.
Martinez has had to constantly contend with Wigan being preseason relegation favourites, but season after season he proves the bookmakers wrong, despite consistently having the smallest squad and lowest transfer budget in the EPL.
Ferguson is a huge fan of loyalty and heaped praise on Martinez in a recent interview. Wigan owner David Whelan has fought hard to keep him at the club and very nearly lost him to Liverpool this summer.
But the Whelan insists he would not stand in the Spaniard's way, should a top-four club come looking. United would certainly fit that model.
Still a long shot, but certainly not beyond the realms of possibility.
Arsene? Surely not!
But why not?
Wenger is considered an elite manager in the game, and quite rightly so. He has a fantastic eye for talent and a knack for developing players into world superstars—just ask Thierry Henry and Robin van Persie.
He runs the business side of the football club remarkably well, while many other European clubs look on with envy as they struggle to manage their huge debts.
On the pitch, sometimes performances can suffer as a result of financial constraints, but Arsenal have never finished outside the top four since he has been at the helm.
Wenger boasts a quite stunning CV and is only second to Ferguson as the most decorated EPL manager of all time.
Only the Champions League eludes him, but that is far from a disgrace. Ferguson knows all about how difficult that trophy is to win.
Wenger's stock may be lower at this moment due to Arsenal's disappointing start to the season, but make no mistake: They'll be back in the top four sooner rather than later.
Ferguson and Wenger have certainly had their run-ins over the years, but they have recently settled into a mutual respect for one another.
If Wenger does leave Arsenal, his name will be touted by every top European club, but the Frenchman could want one more shot in the EPL.
What's left to say about the self-confessed "Special One" that hasn't already been said?
Egotistical? Yes. Arrogant? Yes. Aggressive? Yes. Irritating? Yes. Plays mind games? Sure.
But is he a winner? Most definitely.
Many people in this world talk the talk, and Jose Mourinho is most certainly one of them.
But few can back it up with results, and the 49-year-old is one of those who can.
Success has followed the Portuguese manager wherever he's gone, ever since he learned his trade under Sir Bobby Robson at Barcelona.
He loves pressure; in fact, he invites it. Many feel Mourinho loves his own hype, and to an extent that's true, but it also serves as a fantastic distraction so that his players can prepare for big games without too many distractions.
He is a clever man and has the media eating out of his hands.
Ferguson has grown to admire Mourinho, and the two have plenty of respect for one another.
He has dropped some huge hints that a return to England will happen very soon, and the challenge at United may be too good to turn down, should he be approached for the job.
Ferguson has recently said Mourinho will be one of the people he will recommend when he decides to step down.
Guardiola is the only man who is currently available for work, after his shock resignation as Barcelona boss last season.
He's seen by many as their No. 1 target, with Chelsea making no secret of their admiration for the Spaniard.
However, Guardiola is in no rush to make any decisions and is currently in the middle of a one-year hiatus from football altogether.
Guardiola developed a team-playing style at Barcelona that is arguably the greatest ever seen.
Such has been Barcelona's recent dominance, Guardiola has already won everything he possible could.
In just four seasons at Camp Nou, his honours far outweigh most managers who have been in the game for 40 years.
Three La Liga championships, two Copa del Rey's, three Super Cups, two Champions League titles, two UEFA Super Cups and two World Club Cups, to name but a few—and that's not mentioning any of the twenty individual honours he has received as manager.
He's one of the favourites, and quite rightly so.
Definitely not the sexy choice, but could well be the right one for a number of reasons.
Ferguson may be an advocate for Mourinho, but the Scotsman sees David Moyes replacing him at the helm of Man U.
He has done an amazing job at Everton on a shoestring budget, and it's understandable why he is one of the best-paid managers in world football.
He's yet to sign a new contract at Everton despite only having six months left on it, which makes interesting reading for the skeptics out there—could a bigger job be on the horizon?
Moyes achieved the unthinkable back in 2004 when Everton qualified for the Champions League, and he has only finished outside the top 10 three times in 11 years, the last being 2006.
Ferguson has spoken of his huge admiration for his fellow countryman, and the two managers are very good friends off the pitch.
And while superstars such as Guardiola and Mourinho will no doubt be the media's favorites, Ferguson would prefer for the manager to not take the limelight away from the team.
Sir Alex is from the old school and loves the no-nonsense approach Moyes brings to the table. Of course, both managers have had to adapt over the years, and these two have more than managed to change with the times.
At the relatively young managerial age of 49, many believe Moyes is in line for a big job, and it could well be the perfect fit for both parties.