"He (Salman) was not laid back at all. On paper he knew he can't afford to be laid back as he had to work hard for this film as he is racing against a steam engine...In wrestling, weight goes up and down. Physically, this film has been very challenging," Ali told PTI.
Even after going through the grueling training sessions and workouts in the gym, according to Ali, the 50-year-old actor never complained.
"Only on hard days he used to say can I have an ice cream... But the day he was done he had four ice creams," Ali added.
The "Bajrangi Bhaijaan" star had to alter his weight from 100 kgs and then as per the instructions of Ali, he came down to 90 kgs and then to 82 kgs.
"At the age of 50 to do all this within six to eight months takes a lot of hard work. Even when he was not working on sets he had to train for four hours. This is phenomenal for an actor enjoying such stardom," he said.
Apparently "Sultan" is the first sports film that Salman has done in his career.
"This is Salman's first sports film and you do make some changes keeping his personality in mind. We wanted to make "Sultan" with him only. Whatever changes happened, it happened on the sets not on script level," he said.
"His understanding and experience helped us to make a better film. He did small changes and not the big things," he added.
The "Dabangg" Khan loves to flaunt his chiseled body on screen and "Sultan" required him to wear "langots", considering the fact that he plays a wrestler.
The "Gunday" helmer reveals that Salman was initially shy to wear a langot.
"He is a very shy guy. He is very conscious about his body. He is the poster boy for everyone in the gym. Salman Khan is the bible of body building," he added.