The 2003-film starred Sanjay Dutt as the lovable goon and gave a new life to the actor's career.
Hirani, however, said the film was originally planned as a TV series and he had approached Madhavan for the titular role.
"Before Munna Bhai MBBS got made into a film, years back I had written it as a series. I wanted to do a serial out of it and that time Maddy (Madhavan) was doing many serials, he was a big star on television and I had approached him and he said 'I am too busy I don't think I can do it'.
To which, Madhavan added, "I always knew it (the film) had a better future."
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The duo was speaking at the trailer launch of film "Saala Khadoos", which stars the "Tanu Weds Manu Returns" actor and is co-produced by Hirani.
The "3 Idiots" helmer also said that he is working on the next script of Munna Bhai.
"Yes we've been working on a Munna Bhai script. We have 4-5 Munna Bhai scripts written but they were never as good as the earlier two so we kept them aside.
The bilingual sports drama "Saala Khadoos" is scheduled to release on January 29.