PSG president Nasser Al-Khelaifi recently stated that the reigning French champions are already preparing for life after the 33-year-old, who has often talked about retiring from the game when his contract expires in 2016.
However, Raiola says the Ligue 1 outfit have no chance of finding a worthy successor to the Swedish superstar.
"It is impossible to replace Ibrahimovic, just like it was impossible to replace Pele and Maradona," the agent was quoted as saying by Journal du Dimanche.
"There does not exist anyone like him. PSG would already have bought him if there was another Ibra."
Raiola also suggested that Ibrahimovic could yet decide to extend his stay at the Parc des Princes.
"Could Ibra sign a new deal? We'll see ... Everything is possible with Zlatan. He is feeling very well in Paris and PSG are still the most exciting project for him."
Ibrahimovic has netted 12 goals in 13 appearances in all competitions so far in 2014-15.