"You have to understand that in the Hindi film industry it's very difficult to star two actresses in a particular film. Like Katrina is in the movie and she is a superstar, then a lot of superstars you want to approach won't agree to do the kind of role Kalki did in the film. There is too much politics," Akhtar said.
However, she has high regard for Koechlin's acting capabilities and feels the Indian actress of French descent fitted the bill for the character she conceived.
"Kalki is a very interesting actress. She is very edgy. Kalki had no such notion. She doesn't come from that school. She's a wonderful actress. I met her through Anurag [Kashyap]. I saw her in Dev D and also the yet unreleased The Girl in Yellow Boots and she is superb in it."
Koechlin is married to Kashyap.
"She has got a very different role. She is not the heroine of the film. She has that sense of comedy and not over the top. I needed that balance in an actress who could pull that off. I needed someone with that sensibility and Kalki was perfect."
Zindagi Na Milegi Dobara is a road trip film, which shows how the lives of three men, played by Abhay Deol, Farhan Akhtar and Hrithik Roshan, change when they go on a holiday.