The ghost of Matt Busby haunted every manager at Old Trafford until Alex Ferguson arrived. Now history is repeating itself as no one can match Ferguson's standards.

By the time you read this, Michael Carrick may be Manchester United's former manager.

Things could hardly be worse. Wednesday was a humiliation. Como are a club few people outside Como would have known much about until recently. Yet there they were, exposing United's weaknesses.

Carrick deserves credit for getting United into the Champions League. But circumstances helped. Their rivals were distracted by other competitions while United had a clear run at the league. To his credit, Carrick made the most of it.

Bruno Fernandes was central to that late-season revival. He is a very good player, though I have always had reservations about his temperament. At his best, he is inspirational. Last season, he was among the finest attacking players in the Premier League and one of the best United have had in years.

This week, Fernandes took aim at Carrick. That is a dangerous moment for any manager. When the captain speaks out, it suggests something is wrong inside the dressing room. The unity has gone. I dislike seeing managers sacked, but Carrick's position looks increasingly untenable.

History is repeating itself.

The truth is that for all their glory, Manchester United have had only two great managers: Matt Busby and Alex Ferguson. Everything that has happened since Ferguson left tells us how difficult it is to replace a giant.

Busby arrived in 1945 at a club still recovering from war. Old Trafford had been bombed. He built one of the great teams in British football, the Busby Babes, and gave United an identity that went beyond winning matches.

His teams played with an adventure that was unusual in English football at that time. More than that, he trusted young players. He believed they could come into the first team and beat the best. That was a revolutionary idea at the time.

United won back to back Leagues in 1956 and 1957 with the youngest team English football had ever seen. Then, a decade after the Munich disaster, they claimed the European Cup.

Busby left the following year, in 1969, but his shadow haunted the corridors his successors walked. They were releated in 1974 - a mere six years after the glory of Wembley and that 4-1 win over Benfica.

Chaos followed. Seventeen years between Busby leaving and Ferguson joining - just three trophies claimed in that period.

Enter Ferguson.

The parallels with Busby were immediately spotted. Both were Scots. Both took time to get success - three years in Busby's case, four in Ferguson's. Each man was seven years in the job before they won their first League.

Ferguson eventually won more trophies than Busby: 13 Premier League titles and two Champions Leagues compared to Busby's tally of five Leagues and one European Cup.

But Ferguson inherited something precious. Busby had established the culture, the ambition and the belief that United could be a great club.

The difference between Ferguson and his predecessors was this. First, he was given time to build something. Second, he thrived under the pressure that underwhelmed others.

The truth is United could not find anyone strong enough to replace Busby for 17 years. And the truth is that they have not found the right man to replace Ferguson in 13 years.

Michael Carrick and Ole Gunnar Solskjaer belong in the tradition of Wilf McGuinness, the former promoted from within and who found the job too much. David Moyes was the Frank O'Farrell of his generation. O'Farrell, a Cork man, had done well at Leicester, just as Moyes did well at Everton. But United were dour under both men. Both tried. Both failed.

Louis van Gaal was the Dave Sexton of the modern era: good coach, good football played by his teams, but incapable of winning the league at Old Trafford.

Jose Mourinho had the personality and ego to command a club of United's stature. So did Tommy Docherty and Ron Atkinson. All three won Cups. But at Manchester United, the league is the ultimate test. None passed it.

Erik ten Hag and Ruben Amorim were regarded as ambitious, progressive appointments. So were McGuinness and O’Farrell in their time.

Reputation elsewhere is no guarantee of success here. The job has consumed manager after manager. Now Sir Jim Ratcliffe, the club’s co-owner, is presiding over a shambles. His responsibility is to make United successful. So far, the evidence is not encouraging.

Why do so many people care when Manchester United are in trouble? Because we love football. And because, whatever our allegiance, we cannot ignore what Busby and Ferguson gave the game. They created teams that meant something to millions of people.

United must find another manager of that calibre. That is easier said than done. Great managers do not appear on demand, and there is no guarantee that the next appointment will be the answer. Carrick may carry the can. But sacking him will not solve the deeper problem.

Last week, Lisandro Martínez spoke out. This week, Fernandes did. The noise around Old Trafford tells its own story. United inspired generations of children to play football. They gave the game romance, ambition and a sense of possibility. That legacy remains.

But the road back is long. And there is no obvious sign that those running the club understand how to travel it.