It is part of tournament regulations that competing teams must make part of their pre-match session open to the media.
Almost always, that takes place at either the ground where the game is being played, or on home soil prior to departure, as has been the case with both United and City this season.
On Thursday, it was confirmed that Real would remain in Spain for their final preparations.
However, those plans have now been altered.
But instead of using Old Trafford as their training venue, manager Jose Mourinho has chosen the Etihad Stadium instead.
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 on Saturday.