Off the pitch, Mbappe has some catching up to do. Ronaldo remains an icon in Madrid, has a hotel bearing the CR7 branding in the city, attracts more than half a billion followers across his social media accounts and even has a galaxy named after him.
But Mbappe, having been the star attraction and huge selling point of PSG during his time there, will be placed on a similar pedestal once he arrives in Madrid.
Before all those bells, whistles and social media debates, the small matter of a Euro 2024 quarter-final.
Neither man has set the tournament alight so far. Mbappe looks hampered by a range of issues – including a broken nose from the opening game against Austria and having to play in the discomfort and distraction of a protective mask.
France’s style of play, as evidenced by their lacklustre last-16 win over Belgium, is characterised by stodginess and a need for everything promising in attack to go through Mbappe. When he is crowded out or out of form, the system does not work – leading to the pre-tournament favourites failing to score from open play in four matches in Germany.
Questions of Ronaldo, meanwhile, focus around whether he should even start after two below-par, goalless showings against relative minnows Georgia and Slovenia, where at times the bright attacking talent Portugal possess seemed actively hampered by the presence of a man more than a decade older than his team-mates.
Will such a grand occasion as this quarter-final bring the best out of one or both of these men? We wait with baited breath.
If it is Mbappe who comes out on top, the journey from doe-eyed child admiring posters of Ronaldo to being the sport’s undisputed poster boy will surely be complete.