In years to come this game may well be remembered as the start of Ryan Giggs' path to managerial greatness. Right now it should serve as a brutal example of all that is wrong with Norwich City in the Premier League this season.

You can blame the former manager and his cautious outlook to surviving amongst the elite. You can blame the club's board for not acting sooner when Hughton and his staff appeared incapable of halting the slide.

You could even go back further to question the ethos and the thrust behind a record transfer outlay last summer and the failure since to integrate highly-rated commodities into a formula that propelled the club from League One and sustained them in the top flight. They are all ingredients in a toxic mix to untangle a mess of the Canaries' own making.

Norwich must now realistically try and halt title-challenging Chelsea and FA Cup finalists Arsenal, along with relying on results elsewhere after Sunderland wrestled back control of their own destiny by hammering Cardiff City over a desperate weekend.

You do not need to be a mathematician to assess the probability of such an unlikely sequence of events unfolding over the coming days.

What the Canaries served up at Old Trafford is what they have delivered for the majority of a season that started with so much promise and has descended into inexorable decline.

Norwich resisted for 40 minutes with a cohesive stubbornness that raised genuine hopes they could spoil Giggs' first day in charge of the club he has served with such distinction.

The tumultuous reception and the fervour that greeted the arrival of a favourite son had largely dissipated in the face of Neil Adams' impressively robust tactical formation and the visitors' starting line up.

But it took one cross to evade three Norwich players and Steven Whittaker's frantic attempt to repel Danny Welbeck for that fragile belief to dissolve and the brittleness which defined Hughton's tenure to re-surface.

Wayne Rooney sent his England colleague John Ruddy the wrong way from the penalty spot in the closing moments of an opening period where Norwich had looked anything but a lost cause.

Yet the scale of the implosion following Rooney's second, within minutes of the restart, evoked painful memories of those recent surrenders at Southampton and Aston Villa, when too many of Norwich footballers looked disinterested and dispirited; unable or simply unwilling to accept personal responsibility for their part in another hammering.

City's retreating players invited Rooney to advance unchecked before he underlined why he is the best domestic player of his generation with an unerringly accurate finish guided around the sprawling Ruddy.

Giggs' response was to unleash Juan Mata from the bench; a Spanish international with a huge pedigree to match the stratospheric price tag. City's collective reply bordered on negligence - the World Cup winner was allowed not once but twice to escape detection deep inside their own penalty box to despatch cut-backs from United's right-flank.

It was a capitulation to set alongside the white flag hoisted across the city at the Etihad before Christmas. Ruddy's shot-stopping defiance and United's profligacy prevented a heavier reverse. City could only muster sporadic attacking flurries laced with a familiar lack of conviction.

Adams' internal promotion brought a positive uplift on a set of under-performing young men, but he is no miracle worker. This group of players possess glaring deficiencies and vulnerabilities.

There will be those who justifiably argue such negative traits were accentuated by the flaws of the previous management, but Norwich's squad can not hide behind that excuse now. Adams' refreshingly adventurous approach to an epic task fails to disguise the weaknesses he inherited. Norwich concede too many goals and show little or no sign of being able to consistently plunder at the opposite end.

That is why they have now slipped below the waterline. That is why they have lost five consecutive league games and won only three Premier League matches since December 7. That is why the attainable goal of top flight consolidation now appears beyond them.

Norwich took six years and endured much heartache and financial pain to return the last time they exited the Premier League. Should they lose the fight and fail to overcome the odds stacked against them they will undoubtedly be in a much stronger financial position to deal with the cold reality of Championship football. But in a season defined by missed opportunities and chronic inconsistencies this will be the greatest spurned opportunity of them all.