The phoney war midway through the mouthwatering last-16 tie, delicately balanced following a 1-1 draw at the Bernabeu last month, took a twist with confirmation that Jose Mourinho's players will hold their final training session at the Etihad Stadium on Monday.
As no explanation has been offered for the switch to Manchester City's home ground, it can only be presumed Mourinho thinks there is less chance of his team being spied upon there than at Old Trafford, where the session would normally be held if it came after departure from Spain.
It would certainly be typical of Mourinho's mindset, and Ferguson's too given United have taken to remaining in Manchester for their eve-of-match training sessions this season, which have to be open in part to the media under UEFA rules.
Yet United manager Ferguson does not require spies to understand how dangerous Real can be, as Cristiano Ronaldo makes his first return to Old Trafford since a world-record £80million transfer to Madrid in 2009.
The Scot saw it at first hand in the Nou Camp on Tuesday, when Ronaldo scored twice as Real tipped Barcelona out of the Copa del Rey.
That performance, in a tie that began in exactly the same position as United's will on Tuesday, was enough to bring Ferguson out in a cold sweat.
And there is still the possibility of more majesty tomorrow given Real host Barcelona in the La Liga Saturday afternoon, in a match brought forward to 1500GMT purposely to give the current champions more recovery time.
"I was shocked," Ferguson said. "Real Madrid were magnificent.
"They were absolutely brilliant, with Ronaldo, Angel di Maria and Mesut Ozil so good on the counter-attack.
"But we already knew Madrid are one of the best counter-attacking teams in Europe. That is what we will be up against on Tuesday and that is what our preparations are centring around.
"We have to make sure their counter-attacking doesn't kill us."
Meanwhile, it has been confirmed a giant mosaic will be unveiled inside Old Trafford on Tuesday, in addition to two surfer flags in a bid to generate an even greater atmosphere.
Flags will also be placed on the second tier of every stand.
No explanation has been offered for why Real are choosing to train at City.
However, Mourinho, like Ferguson, is wary of his training sessions being spied on, either by the media or those with connections to his opponents.
And it seems the former Chelsea boss has decided it is safer to train at City rather than United as they look to claim a quarter-final berth following the 1-1 draw in Spain last month.
Real warmed up with a brilliant 3-1 win against Barcelona at the Nou Camp on Tuesday and face the Catalans once more, this time on home soil, in La Liga.