President Florentino Perez wants to finally add a big-name number to be a totem at the back alongside a star outfield signing.
Although De Gea has been a long-time target for Real, to the point they came within minutes of signing him at the end of the August 2015 window, there is currently a feeling among the Bernabeu hierarchy that Courtois will be an easier - albeit still difficult - deal to do.
De Gea is understood to be very content in Manchester and has gradually become more and more settled. United are not mindful of him angling for a move home in the way that used to be the case.
It is different with Courtois. Having previously played for Atletico, his family live in Madrid and it is his medium-term goal to return there, having only mentioned it in an interview this week. While Chelsea have had confidence that Courtois will sign a new contract, it is not yet agreed.
There is also the fact that United are now in a stronger financial position than the champions, although it would still take a hugely persuasive offer to cause Chelsea to bend. Privately, Perez has told associates that he would expect to now have to pay up to £100m for a top goalkeeper in the modern market.
Real are also likely to offer some big players in any deal, amid what is set to be a summer of significant change at the Bernabeu.
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