Zellweger had never done a musical before, not even in high school or college, so she relished the opportunity. And while hers was one of several Golden Globe nominations the movie received, she says she still considers herself an "impostor."
"This was an extraordinary experience; to learn a new medium of expression is unbelievable," says Zellweger. "Singing makes me feel very vulnerable. Because I had to open that up, say 'Here's my heart. What do you think?' Well, it was scary. And to get through that, something that I had been very, very protective of and closed about for so long. The rest of it was adventure."
And she confidently showed the film's director she has what it takes, because she says she had to. "I went out there and Rob [Marshall] said, 'You just do it, Missy.' And off we went. And then you're on a schedule. And you said you will, so you better. And get to it; you do it. And you're so busy doing that there's no time to really step back and assess how you're doing," Zellweger says.
But when time came for her to watch herself on screen, she says it was hard not to be critical.
"First of all, I have imposter syndrome on a disease level," she says laughing. "And I also have the would of/should of/could ofs so badly."
"I was so proud to be a part of it. It's unbelievable, everything that factors in. And must work simultaneously in order for the take to matter, for it to count, for us to be able to print it. And it's really complicated. And so when it does happen, it's like the Olympics. It's like when you land that vault and it's a "10" because you pointed your toes and everything," she continues.
Zellweger feels the entire cast, including Catherine Zeta Jones, Richard Gere, Queen Latifah and John C. Reily, should all score Olympic, if not Oscar, gold.
"John C.? Who knows John C. can sing like that. Hello, the crooner. And when Latifah comes onto the stage with that fan. Isn't that just - I was floored. I was in my chair and I was squealing. And who knew that Catherine could sing from the balls of her feet? You know? It just comes out. It just keeps going. And Richard Gere? You know? Beautiful," Zellweger says.
She is not that far behind; people are already talking about an Oscar nomination for her work in "Chicago."
The idea sounds nice to her, she says. "It's crazy. It's crazy to me because I feel like the imposter. I'm the imposter Roxie. You know, I didn't start off on the stage and really hope from the chorus and go to the thing. And I have no idea why Rob Marshall got it into his head that this would a good idea. But I am so glad that he did. Because I'm telling you the truth, I wouldn't make the first cut down there on 42nd Street. I didn't go through that process. So it's crazy to me."
Many of her roles have been out on the limb - sort of risky, interesting, delicious and vulnerable. But Zellweger says just doing what she loves is what makes her happy.
"I was an actress when I left Austin. I wasn't doing it on a grand scale, but I was doing it. Couple, few times a year, maybe, if I was really lucky and something came to town. And I loved it. I loved it. And if you get to do it at all, you are successful. So I was a happy girl. You know, I was successful because I got my job every now and then. I was hoping for a continuation of that. This is ridiculous. This is ridiculous.
"And don't ask me how, because people say, 'Tell us about your worse, you know, experience.' There's not one. And this one, this one, right here? My heart is so full from this experience," she says.
"Chicago" opens nationwide on Feb. 7.