McCartney, 74, added that his apprehension doesn't necessarily have to do with fans’ perceiving such an event as a Beatles reunion.
"I don't think either of us have ever thought, ‘Why do it, or why not,’" he said. "It's just that our roads are parallel, with intersections and diversions. He's a great drummer, man. He has a feel that nobody else has. As to going out on the road, it might be complicated."
McCartney discussed a wide variety of topics for the cover story of the magazine's next issue, including whether there is any unreleased music left in The Beatles' vaults.
"There's a few things," he says, though admitting he’s unsure whether the material is worthwhile.
He also talked about his recent collaborations with rap star Kanye West, and explained how West cleverly incorporated a guitar riff McCartney wrote decades ago into the single "All Day."
As for whether he thinks West is a genius, Sir Paul says with a laugh, "I don't throw that word around. I think he's a great artist."
In addition, McCartney revealed that no one in his life has replaced the collaborative musical relationship he had with John Lennon.
"It's very difficult," he explained. "You can't top John. And John couldn't top Paul."