The two-time Oscar winner has revealed that he lacked confidence and asked director Rob Marshall if there was anyone else who could take on the role of Guido Contini, STV reports.
The 52-year-old said: "I did say to Rob in the early stages, 'Is there any way of getting out of this? I have a list of actors who could do it tomorrow!' He tried to convince me I could sing and I said, 'You've no idea if I can sing or not!'
"I sang feebly a couple of times, and on the grounds of that Rob managed to convince me it was worth pursuing."
The actor also said that dancing was difficult because his body is so "creaky".
Day-Lewis added: "I can do a lot of stuff, I can climb, I can run, I can cycle, I can box, but I can't dance.
"I used a lot of 3-in-1 to lubricate those stiff joints. It's not natural grace - that's sheer effort of will. My limbs are a mass of scar tissue through years of doing things I shouldn't have."
Nine, starring Day-Lewis, Nicole Kidman and Penelope Cruz, is to be released in the UK on December 18 and in the US on December 25.