The remarkable Spaniard will play his 60th match at Roland Garros on Sunday when he meets countryman David Ferrer, and a 59th win would give him his eighth title.
Nadal's only defeat came against Robin Soderling in the fourth round in 2009, when he was struggling with his knees and off-court problems.
No man in the history of tennis has ever won eight titles at a single grand slam, but Nadal proved once again with a spectacular semi-final win over Novak Djokovic that he truly is the king of clay.
Murray said: "It's kind of hard to put that in context. It's something that you probably won't see again.
"He's still got a few years left in him as well and I wouldn't put it past him to be in the final a few more times."
The Spaniard has consistently been the fifth best player in the world over the past couple of years but he was won just one of his last 16 matches against Nadal, and that was when his opponent was injured.
Last year Ferrer managed only five games in a one-sided semi-final, but he has at least won a set in both their most recent meetings, in Madrid and Rome last month.
Murray said: "He played very well against him in Madrid and also in Rome. "He had chances, that's for sure. But there's something about that court at the French.
"It's just such a big court and Rafa can create so much angle that it's just very tough for Ferrer. They played in the semis last year and Rafa won very quickly in three sets.
"Ferrer's going to be fresher and he's one of the fittest guys on the tour, and he'll make Rafa work extremely hard. But Rafa's definitely the favourite."
Murray returns to action this week in the Aegon Championships at Queen's Club after missing the French Open with a back injury.
Unlike at most ATP World Tour events, Murray will have British company in the singles, with James Ward, Dan Evans, Ed Corrie and 18-year-old Kyle Edmund all given wild cards, while Jamie Baker is through to the final round of qualifying.
It will be a first taste of the tour for Corrie and Edmund, who on Saturday won his second junior grand slam title in the boys' doubles at Roland Garros.
Murray said: "They need to try and enjoy it and make the most of it. It's not something that happens every day for those guys.
"Kyle's been our best junior for the last couple of years. He's played well at some of the Futures events, he's won a couple, so it'll be a good test for him to see where he's at.
"He's not going to have much time to get used to the grass but it'll be a great experience for him.
"And for Dan, he needs to go out there and give 110 per cent. When he's done that, he's played some very good tennis and had some good wins.
"He's also been preparing on the grass for a while so he'll have more matches than most of the guys."
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