He said: "There's a bit of a love story thread so we really needed someone to sing higher than me. For all Will's good intentions, he can't do it. You need to be female."
Chris also revealed the group's fifth studio album is "dangerously close" to being a musical.
He told The Sun newspaper: "Our new record is sort of a story through its 14 tracks - it's not quite a musical, but it's dangerously close."
The album was recorded in London and Chris has previously said the input of guitarist Jonny Buckland has been particularly prevalent.
Referring to one of the tracks on the album, he said: "'Hurts Like Heaven' is all Jonny. It only has two chords. The songs are group-y, its guitar-y. Johnny is coming out of his cocoon. We're just trying some risky things."