"I would love Manmohan Singh to be the Prime Minister. I think he is very smart man and a genius," he said adding that Rahul Gandhi would be the next best bet.
Khan, who has earlier campaigned for his friends cutting across the party lines, said that Rahul could follow Singh 'when he was ready'.
Earlier, Khan had campaigned for Civil Aviation Minister Praful Patel in Bhandara region in Maharashtra.
He has also campaigned for veteran actor-turned-politician Vinod Khanna, a BJP candidate from the Gurdaspur Lok Sabha constituency in Punjab.