Directed by Sunil Subramani, who has assisted filmmaker Anurag Basu on several films, the movie is said to be a fun love story.
According to sources, Ranbir and Katrina, currently shooting for Basu's "Jagga Jasoos", have only given their voice-over for the song and won't be featuring on-screen.
"All three of them won't feature in that song. It is not an 'item' number. It's a very special song. Ranbir and Katrina have recited poems which will be there in the track, on which Sunny will be dancing," sources said.
"Fuddu" stars newcomers Shubham and Swati Kapoor in lead roles.
Meanwhile, Leone will also be seen in a special number in superstar Shah Rukh Khan's "Raees", scheduled to release in January next year.