It is one thing losing to Wolfsburg, the second best side in Germany last season and an established force in the Bundesliga and in Europe.
It's quite another losing to a Bournemouth side who - as their supporters loved reminding ours yesterday - are from League Two.
In the catalogue of humbling experiences that United have been through since the Sir Alex Ferguson era came to an end you would be hard pressed to outdo those of the David Moyes season but this defeat to Bournemouth would be up there.
Seven years ago, the Cherries were in League Two with a 17-point deduction and United were beating Barcelona en route to a League and Champions League double winning season under Sir Alex.
In a bizarre and unpredictable season that has even made the Special One look normal, there is at least some refuge for Louis van Gaal, but not much.
For all the injuries that have stretched the squad to the limit, this was not a result that any United manager with his resources should ever contemplate.
United could drop out of the top four if Tottenham beat Newcastle today but there are other considerations that will trouble the club's hierarchy much more.
Both in Wolfsburg and again here, we were laborious, predictable and so eminently beatable.
Even our defensive resilience that has made us so hard to beat this season has disappeared.
Even Van Gaal, a man never lacking in confidence, has started to look dazed by the scale of this team's shortcomings having gone five games without a win.
That's two more than the worst slump United went through under Moyes.
Had we won, we would have gone within a point of City in first place but, having lost it, the questions to the manager were about whether he still believes in his side and why he did not bring on Ashley Young.
Javier Hernandez scored a hat-trick for Leverkusen yesterday - that's ten in seven now - and James Wilson has scored two in two for Brighton on loan.
United's goal against Bournemouth was poked in by Marouane Fellaini having taken two paces on his knees and the less said about the usual goalscorers the better.
In the closing stages, Van Gaal replaced Fellaini with Nick Powell who made an unlikely centre-forward.
Anthony Martial was moved out to the right to accomodate Powell who struggled to make an impact and there was no sense at the end of the great United attacking siege we once knew and loved.
Dark days indeed.