The big-spending French champions have been linked with a mega-money move for the prolific Portuguese in recent seasons, with former sporting director Leonardo claiming they "did everything they could" to convince Ronaldo to move in the past.
Mendes, however, believes such a transfer is out of the question and instead believes the 29-year-old could move to America once his time at Santiago Bernabeu is up.
"Ronaldo to PSG is impossible. He will finish his career with Real, and maybe he'll go to the United States. Only God knows," he told Telefoot.
"He's a machine, he's the best player in history and nobody can be his equal. It's not even fair to compare him to others. He's a winger, right? Tell me the names of wingers that have scored even 10 per cent of his goals."
Mendes admits he has a good working relationship with PSG president Nasser Al-Khelaifi but believes French football remains firmly in the wake of the Premier League and La Liga.
"Nasser is my friend, I enjoy a good relationship with him. He does some good work at PSG, who are one of the best clubs in the world right now," said the Portuguese.
"Ligue 1 is good, but I think the Premier League and La Liga are better, even if PSG have bought some quality."
Supporters of Ligue 1 side Monaco were left incensed in the summer when Mendes helped to broker an €80 million deal to take James Rodriguez to Madrid, but he is adamant the player is where he wants to be.
"The people who decide are the players and the clubs. James is happy today because he was dreaming of Real Madrid. That's what counts," he said.
Mendes, now 48, also suggests he could take charge of a club himself in the future - possibly when Ronaldo chooses to retire from his playing days.
"I'm on the phone 17 to 18 hours a day. Sometimes it's difficult, but it's my life," he added.
"Club president? Why not? I think I have enough experience to do it. But right now it is too soon. Maybe I'll wait until Ronaldo stops, so we could stop together."