Carrie Underwood is "doing good" on 'American Idol'

Luke, 48, told 'Extra': "Carrie and I had always been in the business together, but we never spent much time together.

"So to sit behind the desk and watch her really learn how to transition out of being the winner of 'American Idol' and a superstar to, like, being the judge at the table ... she's doing good."

Carrie actually won the fourth season of 'American Idol' back in 2005, and Luke has jokingly claimed that he doesn't want Carrie to "pick up any of [his] habits".

The country music star added: "I don't want to influence her in any way."

Meanwhile, a source previously suggested that Carrie "couldn't say no" to 'American Idol'.

The award-winning singer felt like she owed a debt of gratitude to the TV show, which helped to catapult her towards stardom in the music business.

The insider told DailyMail.com: "They have asked Carrie in the past to be a judge and either timing, money or other commitments have got in the way to make it a reality.

"She has been asked to coach on 'The Voice' as well, but it just never seemed right.

"Even with the opening she has to speak to the same people at NBC by working with 'Sunday Night Football', she has always felt that she needed to be loyal to 'American Idol'.

"She has always monitored the show that started her career, and now she couldn't say no."