Shah Rukh Khan was the first choice for the role of Munnabhai, but was forced to turn it down when he had back problems.
But when Shah Rukh Khan was part of the film, he helped out with the script. The producers credited him for his consulting inputs. After SRK, Vivek Oberoi was considered for the same role but Sanjay Dutt finally won it.
SOURCE - TIMES OF INDIA