Carrie Underwood "wasn't really interested" in performing the 'Sunday Night Football' theme song when it was first offered to her.

The 41-year-old singer has performed the NBC theme song for over a decade now - but Carrie actually rejected the opportunity when the idea was first put to her.

Fred Gaudelli, the executive producer of NBC's NFL coverage, told Yahoo: "We reached out to Carrie, she wasn't really interested."

Carrie admitted that it simply "wasn't the right time" for her.

However, the blonde beauty did finally accept the offer in 2013 and she's relished the experience ever since.

She said: "I feel like [NBC] do such a great job year after year of reinventing and reinvigorating the open.

"People know it's very comforting to see the open and kind of have a general idea of what it's gonna feel like. But the way that they go in every year and do what they do to keep it fresh is really cool."

Fred also revealed that he said to Carrie to convince her to accept the offer.

He recalled: "I said, ‘Look, we're the No. 1 show in primetime television. This is going to air in front of 20 million people plus every single week.’ [Carrie's] a football fan, I think it's kind of a natural [choice].

"I showed her the demographic breakdown, and once that was done, she's like, 'You know what? You're right. We should do this.' And that began a now 12-year run."

What's more, Fred insisted that there haven't been any "creative differences" between himself and Carrie.

He shared: "Carrie and her stylist play a big role in that because she wants to change it up every single year and look a little bit different. We've never really had any creative differences."