Mbappe arrived at the club from Monaco in 2017 on an initial season-long loan before making his stay permanent a year later.
Florentino Perez has also been working towards this transfer for some time too, reducing the Blancos' wage bill and splashing less cash on new players in recent windows, not just because of the economic crisis caused by Covid-19, but also as a way of making room for Mbappe.
That leaves the door ajar for a spectacular U-turn.