We all knew this day would come. Perhaps it has come a little sooner than people might have hoped, yet here it is.

After 26 and a half years, 13 Premier League trophies, five FA Cups, four League Cups, two Champions League trophies, one Cup Winners’ Cup, one FIFA Club World Cup, one UEFA Super Cup, one Inter-Continental Cup and ten Community Shields, Sir Alexander Chapman Ferguson is to step down as manager of Manchester United.

On 19th May, Sir Alex will take charge of his 1,500th and final game as United manager away at West Brom, ending with a win ratio of almost 60%.

That statistic alone is pretty incredible when you look back to where it all started for him in 1986. His first match in charge was a 2-0 defeat away at Oxford United. He didn’t win his first trophy until 1990 and his first League title did not come until 1993. Had this been within the last decade, Fergie would have lost his job a long time ago.

Yet since that first trophy, what he has achieved at Manchester United is nothing short of miraculous. He has single-handedly taken the club from mid-table mediocrity to the greatest ever English team; the ultimate force; the team that everyone wants to beat. Since the founding of the Premier League over twenty years ago, United have never finished lower than third.

He is a man who has divided opinion down the years, but whether you like him or not, it is impossible to deny him his place as the greatest football manager of all time.

There have been many changes in recent years at Old Trafford that have raised questions about the stability of the club. Ownership of the club has changed hands, sponsorship has changed and world-class players have come and gone. But through all the trials and tribulations, one thing has remained constant (apart from the seamlessly everlasting career of Ryan Giggs) and that is the manager.

Ferguson has always been the one person at the club that fans, players, board members, directors, owners and shareholders could rely on. He has always been the calm in the storm. Now that the club is coming to terms with his imminent departure, who can they turn to now to be the calming influence?

Ferguson’s departure will have significant consequences for Manchester United. While the club remain one of the giants of world sport, they no longer have that stability that they have relied on for the last 26 and a half years.

And the question now is, where next? How could they possibly replace somebody like Sir Alex?

Well, the simple truth of it is, they can’t. Frankly, there is not a single football manager out there who could possibly replace Sir Alex. No manager out there is capable of emulating the success that he has achieved.

Now that’s not to say there aren’t some fantastic managers out there, because we all know that there are. But the landscape of the modern game has changed, making it virtually impossible for a manager to stay at a club even half as long as Ferguson has.

In today’s modern era of impatient owners, one poor season can cost a manager their job, regardless of how long they have been at the club. Ferguson himself had some poor seasons at Manchester United. Just last season, United failed to win a single trophy (apart from the Community Shield), but because he had already been at the club for so long and brought unprecedented success, sacking him for one bad season would have been completely illogical.

Up until today, Manchester United had been living in an alternate reality. Whilst most clubs fail to hold on to a manager for more than three or four seasons, Manchester United have never had this problem. Now they do.

The new manager, whoever that may be, could have two or three good seasons, then all of a sudden, go an entire season without winning a trophy. Who are the owners going to blame? The manager won’t have been there long enough to justify his position, therefore the blame will be placed firmly at his feet.

Bar a couple of notable exceptions, that is the way the modern game works now. No manager is safe. Jose Mourinho is probably the only manager in the world right now who you would never dream of sacking. But the man is so flighty, if he were offered the job at Old Trafford, he wouldn’t stay there for more than five years.

Whoever comes in to the hot-seat, whether it be Mourinho, or David Moyes or whoever, they have their work cut out straight away. Why? Because they are not Sir Alex Ferguson.

The legacy that Ferguson is leaving behind has made it almost impossible to find an adequate successor.

But that does not mean that the new manager can’t enjoy a long, successful spell at the club. After all, they will have the money and facilities that most managers can only dream of. One can only hope that the club’s owners learn from their experience with Sir Alex and not go jumping the gun at the first sign of failure.

As another league season draws to a close, we have once again witnessed a season where managers have  come and gone at the drop of a hat. It’s almost second nature.

But no managerial exit bares the same level of significance as this. This could be the signal that the most successful era of the greatest English club of all time could be coming to an end.