Ferguson missed his side's Carling Cup clash with Scunthorpe on Wednesday as he was in Valencia - United's next Champions League opponents - but the Old Trafford boss kept a closer eye on the Atletico Madrid keeper.
Ferguson's scouts have been monitoring 19-year-old De Gea for some time as the Scot looks for a long-term successor to Edwin van der Sar.
Teenage dreams: Keeper De Gea has been on Ferguson's radar for a while
The 39-year-old Dutchman is on a one-year deal with a guaranteed extension if he plays 30 senior games.
De Gea would cost around £12million and it would be a clever piece of business as his value would only rise.
The teenager, who just missed out on Spain's World Cup squad, has played in the Europa League this season but would be able to play in the Champions League if he joined United in January.
De Gea's Atletico side drew 1-1 with Valencia while United beat Scunthorpe 5-2.
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