A 1971 letter has revealed that John Lennon believed he could make Eric Clapton a greater musician than ever. The handwritten note could sell for $30,000 when it goes to auction next month.

Clapton first met the Beatles in 1964, while he was a member of the Yardbirds. He later played on George Harrison’s 1968 Beatles track ‘While My Guitar Gently Weeps.’ The following year he became part of the Plastic Ono Band alongside Lennon and Yoko Ono.

In the letter, dated September 29, 1971, Lennon says: “Eric, I know I can bring out something great, in fact greater, in you than has been so far evident in your music. I hope to bring out the same kind of greatness in all of us, which I know will happen if/when we get together.”

Auctioneer Joe Maddalena believes the note demonstrates just how close Clapton came to becoming a member of the Beatles. He tells Jam: “There was a point in time when George thought about leaving, and his replacement was Eric. This letter is a link of what could have been.”

The Profiles In History auction takes place on December 18 in Los Angeles..