Mundo Deportivo now report that a clause in his contract could see him terminate his stay in Paris in June 2020.
PSG bought Neymar for a record £198million, but a rescission in his deal means he is free to negotiate an exit after three full seasons.
The 27-year-old Brazil captain has openly flirted with a move out of Ligue 1, while Los Blancos stars have talked up the prospect of him playing at the Santiago Bernabeu.
Last month, Casemiro described Neymar as in the “top three” best players in the world.
The midfielder, also talking about Vinicius Jr, added: ”
“We’re talking about two great players, two players who are exceptional,” said Casemiro.
“It is up to the coach to talk about whether they can play together or not. There’s no doubt they are great players.
“Of course, they can play in any team in the world.”