Neymar only joined PSG last year in a world-record £200m move, but he is reportedly unhappy in the French capital and eager to return to Spain.
Madrid have long been linked with the Brazilian, initially missing out to Barcelona for his signature from Santos, but Marcelo expects his compatriot to don the white shirt at some point in the future.
The full-back has also rubbished suggestions that Cristiano Ronaldo could look to block the move and insists that there is no reason why Ronaldo and Neymar could not be at the club together.
"Cristiano doesn't own Real Madrid so if the president wants to sign somebody he will do it," Marcelo told reporters.
"If Cristiano stays, does that mean that Neymar can't come? We all want Ronaldo to stay and Neymar has our doors wide open.
"Madrid always have to find the best players and I think Neymar will play for Real Madrid one day."
Neymar has been sidelined with a foot injury since February, but was recently handed a cameo during an international friendly with Croatia as he continues his recovery ahead of this summer's World Cup.