Khan, whose latest outing "Jab Tak Hai Jaan" is a big hit at the box office, took to his twitter account to wish Singh on his 77th birthday.
"Bhaag Milkha Bhaag" has been directed by Rakeysh Omprakash Mehra and stars Farhan Akhtar.
"I am a big fan of Milka Singh... Wish him all the love and cant wait to see Farhan Akhtar's and Rakeysh's interpretation of his life and time," Khan, 47, tweeted.
Farhan is playing the titular character of Milkha. He also met Singh briefly to prepare for the role.
"Happy birthday to the Flying Sikh, Milkha Singh, himself... May you and your legend continue to inspire us forever," Farhan, 38, tweeted.
The film will hit theatres on July 12 next year.