The 24-year-actor made his film debut in 2008's romance Jaane Tu... Ya Jaane Na.
Bhansali told Hindustan Times: "I saw him in Jaane Tu... Ya Jaane Na; he had a small role but left a great impression. He's been seen in other small parts, but this is his first big role.
"It's a very difficult and unusual film, and to perform in this genre and bring the characters alive is not an easy task. But it came naturally to him.
"There's not much ego in him right now. He hasn't become a full-fledged star yet. When all that comes in, you lose your innocence and start getting corrupt."
The Guzaarish director denied that Ranbir Kapoor had been the first choice for the film.
"Ranbir is my favourite bachcha (kid). He is a part of something that I created in Saawariya. He is very dear to me," the director added.
"So, whenever you make a film, you always feel, 'Let's think of Ranbir in the role or what if Ranbir is roped in for the part?' So, it's not that we offered him the role seriously and he turned it down."
In September, Prateik dropped his surname Babbar after a fall-out with his father Raj, an actor-turned-politician.
Prateik stars in the film with the award-winning actress Kalki, who starred in the independent That Girl in Yellow Boots.