By full-time he was back in one of those cold-sweat, pre-1993 moments, defeated by a football club, actually a football institution, who made his own look puny. Where does he go from here?
This has been far from being a bad season, don't get me wrong. First and foremost we should bear in mind that this season Manchester United have done everything asked of them except win the Champions League and the FA Cup. They made light of the demands of the Fifa Club World Cup, they saw off the best challenge in 19 years from a Liverpool team and all the emotion that entails. They came back in games against Stoke City, Aston Villa, Sunderland and Tottenham when it mattered.
They are hardly the dysfunctional, bickering side that could not make it out the Champions League group stages in the winter of 2005, Ferguson's lowest point in the recent past. They have won three consecutive Premier League titles and any analysis of how bitter their humiliation at the hands of Barcelona was on Wednesday night should be placed in the context of another astonishingly successful season.
But wednesday night, something was missing. The usual inertia on the United bench when Lionel Messi's goal went in on 70 minutes — Ferguson and his assistants sat slumped like moody teenagers at a bus stop — told you that on this night they had run out of ideas. No-one could argue that Ferguson should rip it up and start again but a new standard has been set by Barcelona and the old Scot would not be doing his job if he did not ask himself how he can reach and surpass it.
You can't have what Barca have got ? The preoccupation now will be Xavi Hernandez and Andres Iniesta, very much the men of the moment. How do United get their hands on two pocket-sized demon midfield passers? How much will it cost? Can they get a Messi too? But trying to replicate exactly another team's model for success, even trying to replicate the model of past United team's success, is dangerous.
Once the theory was that United would never prosper without a new Roy Keane in the middle of midfield. You don't hear that much now. Instead, Ferguson put his faith in equally dominant players, like Cristiano Ronaldo and Wayne Rooney, who are just as effective only in different ways, in different positions. Ferguson cannot conjure another Xavi or Iniesta, but United need more of those dominant midfield players.
Who can make this United team stronger?
As befits a team that looked so competitive until now, this summer Ferguson has been linked with precious few big-name players. The interest in Karim Benzema at Lyon is longstanding, so too that in Antonio Valencia at Wigan Athletic and Bayern Munich's Franck Ribery.
These are all dominant players, they are not comparable in style to Xavi and Iniesta but then who is? Those two are a real one-off, once-in-a-generation players and attempting to find clones of them would be foolish. Ferguson's policy has always been to buy the best players he can attract to United and trust they will flourish on the biggest stage.
Will Owen Hargreaves be the same player again?
It took a couple of takes to deduce the identity of the bloke on the touchline before the match with curly black hair in a United club suit. A third Da Silva brother perhaps? It was the long-lost, lesser-spotted, too-often injured Hargreaves. One of the stars of last year's final in Moscow, he has not kicked a ball for United since 21 December and last night, for the first time in a while, United were missing him.
The notion that Wednesday's result would have been radically different with Darren Fletcher in the United side is hopelessly optimistic at best. With Hargreaves rather than Luis Anderson you could see a case for United having more energy in central midfield. Hargreaves has been brilliant in patches for United but at £17m he owes Ferguson a big season in 2009-2010.
What do you do with Ronaldo?
On the occasion of one of his greatest disappointments, the behaviour of Ronaldo was encouragingly gracious. On more than one occasion he glanced up at the stadium's big screen for a glimpse of that face he loves more than any other. He swerved a handshake with Carles Puyol as the Barcelona team applauded United up the steps but that was understandable. He never gave up on a pretty wretched night.
A logical mind would say that joining Real Madrid now is an even greater folly, so lost in Barcelona's shadow are they. But if Ronaldo's reasons for staying at United were that they were Europe's premiere team, then Wednesday night has weakened that premise. Yet for all his histrionics, Ronaldo has never been less than professional. If he turns up at United next season there's no reason to doubt he will probably end up top scorer again.
How long can Paul Scholes and Ryan Giggs last? With these two United giants now facing surely their last season at the club they handover to a new generation who have an unprecedented chance to establish themselves.
When do we get to see the £7m Zoran Tosic his fellow Serb Adem Ljajic who arrives next January, around £3m? For these young players as well as Darron Gibson, Danny Welbeck and Federico Macheda the door is open. Adam Johnson of Middlesbrough is another Ferguson is understood to be interested in.
If they have to face Barcelona again next season then United will have to learn from Wednesday as they did with their semi-final defeat in 2007 to Milan, whom they subsequently eliminated the following season. The trouble with Barcelona is that they are better and younger than that Milan team and they could be around for a while yet.