The 42-year-old star, who has previously released duets with her Moulin Rouge! co-star Ewan McGregor and British singer Robbie Williams, insists she hates performing in front of people and had to be persuaded to sing in new musical movie Nine.
She said: "I was terrified of it. I am not a natural singer in the sense that I don't love getting up in front of a group of people and just belting out a tune. It needs to be coaxed out of me because I want my voice to tell a story and sometimes it doesn't have the capacity to do that."
The actress felt particularly pressured because director Rob Marshall had told her he envisaged her appearing as a "goddess" in the movie.
She told Empire magazine: "When Rob approached me, he told me a role had been written especially. He told me he wanted her to look like a goddess and I was a little overwhelmed by that."
While Nicole was eventually persuaded to record her vocals, she has previously vowed never to sing with her husband, country music star Keith Urban.
She said: "We have our work, but most important is our life together, we don't want to blend the two."