The form for visiting managers at Old Trafford is to bring a bottle of something decent for their host.
Jose Mourinho turned up last Tuesday with a handy Portuguese red; Harry Redknapp and Sam Allardyce always come armed with a well-cellared claret. It is part of the ritual, the unspoken homage to the godfather of the managerial cabal.
However, in the unlikely event of Rafa Benitez bringing a bottle with him tomorrow as a gift for Alex Ferguson, it is far more likely to contain vinegar. As muscular as the rivalry on the pitch will be, it will carry but a hint of the friction between the two managers.
Benitez and Ferguson do not get on. For them, tomorrow will be personal. Across 13 meetings, eight of which have been won by the Scotsman and four by the Spaniard, the rancour has fizzed just beneath the surface, a perfunctory touchline handshake the extent of their contact.
These are not men inclined to displays of mutual respect. Largely because there is none.
In the past, Ferguson has implied that the Spaniard is deranged and has declined to pass comment on his actions saying he was not sufficiently familiar with the writings of Sigmund Freud.
For his part, Benitez has refused the opportunity to congratulate Ferguson for winning the title, has stated on record that Arsene Wenger is the leading manager working in England and, in a tirade in 2009, claimed the United boss' manipulation of the English FA and intimidation of match officials were both "fact".
No, there will not be any back-slapping tomorrow; the two are not mates. Yet, Benitez suggests it was not always thus. In a recent interview, he recalled a genial meeting in a bar ahead of the 2006 Champions League final in Paris. No growling disdain then, just a lengthy chat about football.
The problems began, he insists, when he turned Liverpool into title contenders the following season. Then, the coolness settled. Ferguson's approach to him was exactly the same as it was to Wenger, he claims. As long as he offered a challenge, the Scot would seize every opportunity to alienate.
Ferguson will see it differently. After all, he has always got along with Mourinho, however much the Portuguese once threatened his domestic hegemony.
And Ferguson will insist he was magnanimous to the other man's success, the first to send a congratulatory note when Liverpool won the Champions League in 2005.
Where relations first soured was after Liverpool tried to sign United's Gabriel Heinze in 2007. For Ferguson, there was nothing personal in it; he blocked the move simply because of the historic gap between the two clubs.
For the sake of his supporters' blood pressure, the United manager wanted Phil Chisnall to remain the last player to move directly between the two clubs back in 1964. Benitez, though, saw the refusal differently. He thought Ferguson's action petty, spiteful and purely engineered to stall Liverpool progress.
From there, Ferguson bridled at Benitez's obvious disdain for English football's masonic order of management. He fumed when his rival attacked his friends in the game, calling David Moyes' Everton a small club, and allegedly showing disrespect to Allardyce when Liverpool easily beat Blackburn.
And the senior manager has long mocked Benitez's lofty reputation for tactical acumen.
"I remember a few years ago when Liverpool beat us 4-1 at Old Trafford," Ferguson said. "That genius Benitez said they had planned to beat us by playing long balls behind us. Remember that? Clown."
There has been little sign that Ferguson's feelings have thawed. He recently suggested Benitez was lucky to find employment at Chelsea and has only ever won things on the back of his predecessors' work.
There was no hint of solidarity for the manager now cast adrift in the Stamford Bridge snakepit in his withering refusal yesterday to "kick a man when he is down".
So Benitez will find himself alone on the touchline at Old Trafford, spurned by supporters and opponents alike, reliant solely on his capacious reserves of self-esteem.
But his isolation will not diminish his motivation. Were Chelsea to stymie United's double ambitions tomorrow, then, as another of Ferguson's previous rivals once put it, he would love it. (© Daily Telegraph, London)