The wild gossip comes from Spanish outlet Diario Gol (DG), claiming that Real have identified Lukaku as a younger alternative to 30-year-old Benzema - incidentally, the Frenchman no longer has great fellow countryman Zinedine Zidane fighting his corner at the Bernabeu.
The rather complicated story alleges that Real remain unprepared to meet Ronaldo's request of a new contract worth €45m per year, a proposed deal that would see him out earn Lionel Messi and become the world's highest paid player once more.
But it is said that Real will only pay him €25m plus another €5m in bonuses. The club is apparently taking account of Ronaldo's age and the impact on the dressing room - his attitude is described as 'incendiary to the squad' and president Florentino Perez has apparently been warned about succumbing to his requests by other players, of whom only Isco is named by DG.
If Ronaldo is to stay, he will become the club's new central striker, replacing Benzema in the team. But the other option is to have super agent Jorge Mendes find a buyer and let him go, with Manchester United unsurprisingly the first destination the report from DG settles on.
And while it is claimed that United would want Ronaldo, who still holds the club dear for the six years he spent at Old Trafford from 2003 to 2009, Perez has a 'counter offer' that would go beyond simply selling the five-time Ballon d'Or winner back to his old team.
It could never be that simple where Los Blancos are concerned.
That is because Real, who would be in the market for a new 'number nine' if both Benzema and Ronaldo are to leave the Spanish capital, would demand that Lukaku is part of the deal.
Where this all falls down - you surely knew it would - is that United will not sell Lukaku. Along with Paul Pogba, he is said to be the player that the 20-time English champions are most committed to keeping. The club invested up to £75m just last summer and got 27 goals straight off the bat from the Belgian in his first season.
If United won't play ball, DG claims Real would then offer Gareth Bale, a player never not linked with a move to Old Trafford, and would ask to have Pogba in exchange instead.
You can see where this is going can't you?
And because none of that will happen, DG has ultimately settled on Real chasing 19-year-old Paris Saint-Germain star Kylian Mbappe. In that scenario, Ronaldo is once again involved in some kind of 'if you scratch my back, I'll scratch yours' exercise between the two clubs.