Life of Pi star Irrfan has previously worked with director Tigmanshu for Paan Tomar Singh.
[Left: Irrfan Khan / Right: Saif Ali Khan]
"The film basically has Saif Ali Khan as the central protagonist. Though he has started shooting for the film with Tigmanshu, Irrfan is yet to join them," a source told Bollywood Hungama.
"[Irrfan] is playing an important part, but he is yet to be given a detailed briefing about what is expected out of him."
Irrfan added that he also does not know what is expected of him in the film role.
"That's because Tigmanshu asked me to do the film and I am doing it," he explained. "I have not really started thinking about it, though. I start investing in a film when [the] time comes, as I don't multitask.
"I will start concentrating on Bullet Raja when [the] time comes."
The international actor recently said that he is not planning to bulk up like his fellow Bollywood stars.
Irrfan will soon be seen opposite Arjun Rampal in the action film D Day under Nikhil Adhvani's direction.
He has described himself as a part of the '1,000 crore club' because of his Hollywood film roles.
Watch a featurette for Irrfan Khan's latest movie Life of Pi: