Joshi has started working on a script based on the athlete's life post retirement. He plans to direct the film too.
"I got interested in how Milkhaji shares such a beautiful relationship with his wife and son. In 'Bhaag Milkha Bhaag' we have only documented his career, but I felt there was so much more to the man than just his professional endeavour," Joshi said.
Joshi is also keen to capture Milkha's relationship with his son Jeev, a successful golfer, on celluloid.
"Farhan has stunned everybody, including Milkhaji. If things work out, he should be a part of the film I write," the lyricist-writer said.
'Bhaag Milkha Bhaag' is directed by Rakeysh Omprakash Mehra and releases on July 12.