Supersub or starting, Henrik will benefit United
The benefits of secrecy are rarely more clearly illustrated.
It is not the first time Ferguson has shown such persistence in signing a long-term target and refused to be deterred by their advancing years.
Manchester United supporters may not regard Laurent Blanc as a particularly auspicious precedent, but Edwin van der Sar certainly is. With a title challenge propelled by five players enjoying Indian summers - Van der Sar, Gary Neville, Paul Scholes, Ryan Giggs and Ole Gunnar Solskjaer - the addition of a sixth, in Larsson, possesses logic.
Nevertheless, it is rare that the recruitment of a 35-year-old attracts almost universal approval. That it has is a sign of the revival of Ferguson's fortunes as well as the enduring popularity of Larsson. It was not long before, however, when talk of a striking signing at Old Trafford would have prompted suggestions of Fernando Torres.
But few have the character to recover from two career-threatening injuries or the ability to change major matches as a substitute; indeed, it is no coincidence Ferguson mentioned Larsson's Champions League-winning cameo against Arsenal in May. The mentality to make the most of life among the substitutes can be rare among players of the Swede's talent.
His capacity to wield influence after a late arrival will be tested at Old Trafford. It is no secret that Ferguson prefers to conduct the majority of his transfer business in the close-season even though Eric Cantona, perhaps his most important buy, was not a summer signing.
In one sense, the January 2006 newcomers Patrice Evra and Nemanja Vidic bear that out with a visible improvement in their second season at Manchester United.
But Larsson is a short-term signing, headed to Old Trafford with goals on his agenda.
The Swede himself described the move as 'fun'. It was an interesting choice of word which suggests that he knows his reputation was secured by earning Barcelona a second Champions League crown; fail at United and it will merely be a footnote on his CV, but this was a challenge he could not resist.
It adds intrigue, too, in an Anglo-Scottish debate.
There have been sneers from south of the border for years, suggestions Larsson's prolific form for Celtic was greatly aided by the poor defences of the Scottish Premier League. Although a succession of imports from the SPL have failed - Barry Ferguson, Lorenzo Amoruso, Jean-Alain Boumsong and Liam Miller among them - it is worth remembering Larsson is in a different class to any.
Perhaps only Brian Laudrup, whose stay at Chelsea was brief and inconclusive, merits a comparison with him.
For United, the addition of the Swede is an admission of the recent paucity of their striking resources beyond the first-choice pair of Louis Saha and Wayne Rooney. It was evident against Chelsea when the bench was populated by defenders Evra, John O'Shea and Mikael Silvestre, plus midfielder Darren Fletcher.
The admission that United misjudged Alan Smith's return from a broken leg suggests he has much to do - indeed Larsson's return to Sweden in March may be well-timed for his eventual recovery - while Giuseppe Rossi's loan spell at Newcastle hardly indicates a player ready to make a decisive impact in the Premiership title race.
And besides an admiration that stretches back several years, Ferguson's decision to add Larsson to his squad is surely based on the feeling that it will not take him long to acclimatise, whether to a new club or a new match; the sense that his football brain and goalscoring instincts remain as sharp as ever.
But, at 35, he is, in footballing terms, pensionable. The announcement of his loan has coincided with suggestions that Andriy Shevchenko, five years his junior, is too old. Strikers who have maintained their finest form in their mid-thirties are a rarity; however the last to do so - and help determine a title - was Teddy Sheringham, then a Manchester United player.
To his advocates, particularly in Scotland, Larsson ranks among the finest goalscorers of his generation. That makes clubs like Barcelona and Manchester United natural destinations, even if the moves were belated.
He helped the former with the Champions League final; for Manchester United, the hope is that it will prove a microcosm of the Premiership title race, decided by a late intervention from the Swede who had started off as a spectator. And if he does, then Henrik Larsson will rank among the best of Sir Alex Ferguson's signings - even if only for two months.