The Spanish defender admitted that Neymar, who made the switch from Barcelona to Paris Saint-Germain last summer, would be more than welcome in the Spanish capital.
Ramos even offered that Neymar may be in the midst of a detour to Madrid in order to avoid the outpouring of anger that would follow if he joined Barcelona's biggest rival directly.
"I like to have the best players, and Neymar is one of them," Ramos said in an interview with El Larguero, as translated by Dermot Corrigan of ESPN FC. "Maybe he thought it would be easier to go through PSG first, rather than straight from Barca to Madrid. I hope so. You never know in football.
"He could bring us a lot of quality. I'd open the door if he wants to come in December."
Reports out of Spain suggested Real Madrid president Florentino Perez has been in touch with Neymar's representatives and that a move could come to fruition in the future.
Since joining PSG, Neymar has scored seven goals in eight Ligue 1 matches to help lift Unai Emery's men into first place with a four-point edge on last season's champion, AS Monaco.
Meanwhile, Real Madrid's title defence is off to a rough start, as Los Blancos find themselves eight points back of Barcelona.