The 63-year-old performer said the US singer will definitely be up there with some of the great musicians that go down in history.
He said to UK newspaper Daily Mirror: 'I love her, she's absolutely amazing. We've become friends. What I like about the Gaga most is that she's amazingly polite and respectful to everyone around her.
'What I loved most about John Lennon is that he was like that. He once gave my mum a lift to the airport and came to my agent's wedding. The Gaga is like that.
'But the greatest thing about her is that she manages to let everyone think they know everything about her but no one knows anything.
'She's a phenomenal star - definitely someone who will be taking on the old sods like me, McCartney and Rod Stewart doing big tours for years to come. Pure genius.'