Jon M. Chu says "the door is always open" for Idina Menzel and Kristin Chenoweth to join 'Wicked'.

The 42-year-old director is at the helm of the upcoming big screen adaptation of the musical, and he'd be delighted to have the original Broadway stars involvement in the movie.

He told 'Entertainment Tonight': "The door is always open. Are you kidding? I'm not gonna say anything.

"I'm not gonna do anything yet, but of course that original cast is amazing. They've been so gracious... They’ve only been supportive and kind."

The film will see Ariana Grande take over Chenoweth's role of Glinda, and Cynthia Erivo will take on Menzel's part Elphaba.

Chenowath recently said: "I feel great about both choices. I have known Grande since she was 10, so Ariana, I am very very proud of you.

"She knows. We talk every day and it’s an honor and a pleasure to pass the wand and the crown to you."

Now, Chu has agreed and insisted everyone "earned" their place in the movie.

He explained: "When you see the new cast, it's pretty awesome. Nobody was offered this role off the top. Everybody had to come and audition.

"We saw everybody in town who could sing. These are tough songs too. Everyone had to earn their position.

"When I say that they came in and blew us away, they earned that spot in every way. It was pretty amazing. It will bring you to tears. Every word means something different when it's coming from their mouth."

Meanwhile, Erivo previously joked she "was not OK" when she found out she had landed the role, and she's started to find some chemistry with Grande.

She said: "I can tell you that Ariana is wonderful. The two of us are really starting to find our feet and find our relationship and really enjoy one another's time and space and conversations. She's the sweetest person."