Kapoor's character in the film, which was previously entitled Silence, has been based on a combination of Charlie Chaplin and Mr Bean.
Speaking to the Mumbai Mirror, a source said that Kapoor wants to look "loose-limbed and flabby for the role".
"For a month until the shooting starts in February, Ranbir will binge on fatty food," the source added.
It was previously reported that Kapoor would also be taking a vow of silence in preparation for the role.
