Not only has Sir Alex Ferguson left his position after 26 years, chief executive David Gill has stood aside as well 11 years after succeeding Peter Kenyon.
Yet there was no power vacuum. For Arnold and executive vice-chairman Ed Woodward have divided up Gill's responsibilities between them.
And a day after Ferguson's exit was confirmed, which itself came on the morning following the first rumours of an impending departure, David Moyes was installed as his fellow Scot's successor.
"To go through the succession we have been through represents a big change," Arnold told Press Association Sport. "The way the transition was achieved characterises how well the club has been run by David and Sir Alex."
Shirt sponsors Aon, experts in risk management, were asked for their input into what, in Ferguson's case at any rate, was one of the riskiest decisions United have had to make for a quarter of a century.
In the end, it was decided to go with the Scot's own belief Moyes was best suited to the role.
"The man widely accredited as having the best judgement in football had a long period of time to think about the inheritance he was passing on," said Arnold.
"He wanted to make sure the squad was in the right shape and the timing was done from a position of strength. That is exactly where the club is.
"When you look at the preparation that went into that and the position Sir Alex put himself in to make that transition, as an example of how to prepare, even down to how we managed the communication around it, it was an exemplary job."
Source: PA
Source: PA