Although the French champions signed full-backs Nordi Mukiele and Nuno Mendes in the summer, they failed to strengthen in central defence.
They have been linked with a move for Inter Milan defender Milan Skriniar, who is also attracting interest from Chelsea and Manchester United, but PSG are also believed to have another defensive target.
According to Marca, PSG have identified Real Madrid's Marin, who has a €30m (£26m) release clause in his contract, which runs until 2024.
Marin is yet to feature for the first-team, but he has made 37 appearances for Real Madrid Castilla - the club's reserved side - where has chipped in with three goals.
PSG are also monitoring the progress of Ibrahima Bamba after sending scouts to watch the 20-year-old feature in Vitoria de Guimaraes's home meeting with Benfica on October 1.