Renee Zellweger was "very afraid" of singing in 'Chicago'.

The Oscar-winning actress starred in the 2002 musical film alongside Catherine Zeta-Jones but director Rob Marshall has recalled how she was frightened of showcasing her vocals on the big screen.

Marshall told The Hollywood Reporter in an interview to mark 20 years since the film's release: "I'd found out that Renee had been a cheerleader in school, so I thought maybe she could dance.

"She came to New York, and (producer) John DeLuca and I worked with her on dancing and could see right away that she could move."

Rob added: "Singing was a different thing. She was very afraid to sing for me. We went to dinner, and I said to her, 'Do you know any songs?' She started singing 'Diamonds Are a Girl's Best Friend' for me in the restaurant because she was so shy about singing formally. I could tell immediately she could sing."

Marshall claims that the 'Bridget Jones's Diary' star was the perfect actress to play the role of Roxie Hart as she had the ability to cover all aspects of the part.

The 62-year-old director said: "Renee was exactly the actor I was looking for because I wanted to find a vulnerable Roxie. Someone who could play the fragile part of her, but then also be a good enough actress to turn the table and become the strong killer that she becomes, and it needed that full range."