Sir Alex Ferguson is arguably the greatest football manager of all time. He's seen it all and won it all with the same club for over 25 years.
Now aged 70, he is still working his magic and is showing no signs of winding down his career. Sometimes it seems like the guy could go on forever.
However, as unlikely as it sometimes seems, he is only human; eventually he will retire. When that day comes, and Fergie is currently saying that that will be in "two or three" years time, Manchester United will, finally, require a new manager.
The seven men on this list, therefore, are the seven men who, right now, look like the best candidates for the job when it might be up for grabs in three years time.
Jose Mourinho is undoubtedly one of the greatest managers currently in the game. The former Chelsea and Inter Milan manager has won the Premier League, Serie A and La Liga, as well the Primeira Liga with FC Porto and the Champions League twice.
He is currently doing wonders at Real Madrid, beating Barcelona to the league title this season and coming a penalty shootout away from the Champions League final.
Mourinho's brilliance on its own would make him seem like the ideal candidate for the Old Trafford hot seat, but "The Chosen One" comes with a bit of baggage.
Aside from the controversy that can, at times, make Sir Alex Ferguson look the teacher's pet, Mourinho does not have a track record of staying put at any one club for an extended period of time.
The best he has managed so far is three seasons and a month with Chelsea, hardly the type of stability that Manchester United will be looking for when Fergie does decide to stand down.
On the positive side, Mourinho's track record of short spells in charge means that there's a good chance he'll be available for hire in the not too distant future.
Sir Alex Ferguson's compatriot David Moyes has been doing a good job with Everton for the last decade.
He has taken a team severely lacking in financial resources to relatively consistent top 10 finishes and has even got his side into the Champions League in the past.
The fact that he's never managed a major European club could well work against him, although on the positive side his relationship with Wayne Rooney has taken a turn for the better recently.
Perhaps the greatest factor working in Moyes' favour is Ferguson's liking for his fellow Scot. Ferguson recently stated that "David Moyes has been unbelievable. I put him in the top six [in the Premier League] because what he's done at Everton has been quite miraculous."
Add in Moyes' solid tactics, a good record in the transfer market and a calm nature and Manchester United may need to look no further than just down the road in order to find their next manager.
Swansea manager Brendan Rodgers is making waves in the Premier League after guiding Swansea City through the turbulent waters of the Premier League with calm and elegant football.
That he did not go running after European football and a bigger transfer budget as soon as it was dangled in front of him is something that should make him more of an attractive proposition to Manchester United.
His loyalty to Swansea is admirable in a mercenary era and is something United will be looking for if they are to find stability in the wake of Sir Alex Ferguson's departure.
On the negative side, Rodgers has only one season of Premier League managerial experience. There is the possibility that Swansea will struggle next season and Rodgers will look like less of a good idea and more like a flash in the pan.
However, Rodgers tactics seem to be solid; his Swansea side has performed well against bigger clubs and his team play the type of passing football that has brought continental sides a lot of success in the last few years.
Soon to be former Barcelona manager, Pep Guardiola is one of the names that has inevitably been linked with the Manchester United job.
Why? Because he's won just about every trophy possible in his four year stint at the Nou Camp. Add in the fact that it's rumoured that he would like to manage in England, and Guardiola looks like less than a long shot for Sir Alex's job.
Being a product of the Barcelona youth system, and a proponent of the that system, Guardiola even has the right ideology for Manchester United, a club that likes to bring players through the ranks and add talent from elsewhere as and when it is required, just as Barcelona do.
A lot does depend on whether or not Guardiola's successor, Tito Vilanova, finds success in Catalonia, just as Guardiola has over the last four years. If Barcelona and Manchester United were both looking for a manager at the same time, it's fairly obvious where Guardiola would consider first.
Manchester United legend Ole Gunnar Solskjaer is currently attempting to make his managerial name with Molde FK in Norway, and things are currently going pretty well for the retired striker.
The Norwegian won the league in his first season in charge of Molde and is currently being courted by Aston Villa, although it does not seem likely that Solskjaer will take the job.
Solskjaer has the advantage of already being more than familiar with the club; he spent 11 years there as a player and served for three years as reserve team manager.
However, so far, the hero of the 1999 Champions League final has no managerial experience in any of Europe's bigger leagues. Whilst this shouldn't rule him out of the job, it does make him more of a risk than some of the other candidates on this list.
There is still a good chance that Solskjaer will end up making a move to a Premier League club before Sir Alex Ferguson steps down, which might make Ole Gunnar a better candidate, or a worse one. Only time will tell.
Current Sunderland manager Martin O'Neill has bundles of experience. He enjoyed an extremely successful stint with Celtic, winning the league three years out of five, as well as a good spell in charge of Aston Villa, establishing the club as top half regulars and contenders for a Champions League spot.
His experience at a big club like Celtic, where the pressure to succeed is immense, as well as his success at clubs with smaller budgets, make him a good candidate for the Manchester United job.
O'Neill also has a good record when it comes to developing young talent, a skill well suited to Manchester United's focus on developing their own players. Ashley Young, Gareth Barry, James Milner and Gabby Agbonlahor have all benefited greatly from spending time under Martin O'Neill's watchful eye.
What works against the Northern Irishman is his age. He is currently 60 years old, and with Ferguson set to keep working for a while yet, O'Neill could be in his mid 60s by the time Manchester United are looking to recruit a new manager.
However, the transition from Ferguson to O'Neill would have a good chance of being relatively smooth. Both managers command the respect of players and know how to get the most out of their squads; their management styles are far more similar than many of the other candidates on this list.
Former Manchester United player Laurent Blanc is currently in charge of the French national side, having previously managed Bordeaux very successfully.
Blanc spent time at United in the twilight of his career, time that seems to have served him well given his flying start to managerial life.
His recent efforts with the French side highlight his managerial ability. Inheriting a job that makes succeeding Sir Alex Ferguson look a little easier, he showed the iron discipline necessary to get his side back on track and has turned them from World Cup whipping boys to a dark horse candidate for Euro 2012 glory.
Arguably Blanc still doesn't have enough club level experience; he has only managed in Ligue 1 for three seasons. However, Bordeaux is a big club, and he is dealing admirably with a squad full of big names at the moment.
Ferguson and Blanc have a good relationship, and Blanc has spent time with the club in the past, factors which could well work in Blanc's favour if he is interested in the job down the line.