The charismatic 60-year-old has been ordered by doctors to remain immobile in a hospital bed with fractured vertebrae and a broken rib after falling on Tuesday at a rally in Lahore ahead of Saturday's general elections.
He addressed by video link the final rally for his Pakistan Tehreek-e-Insaf (PTI) party in the capital Islamabad, where officials estimated that up to 30,000 supporters had gathered.
"God has given you this golden opportunity. Don't let it go. You should give change a chance," he said, looking pale and his voice weaker than usual, as he lay in a blue gown and the huge crowd in Islamabad fell silent.
Tugging at the heart strings of his supporters, he spoke about his Muslim faith, the personal sacrifices he has made and his mantra for reform.
"God will not take me from this world until a new Pakistan is built," he said.
"There should be change in Pakistan and there was no other way to bring change in Pakistan but politics," he said.
"This was very hard. My family was broken," he said, referring to the problems that his British ex-wife faced in Pakistan before they divorced and she moved to England with their two sons.
An AFP reporter said the crowd fell silent, straining to listen to Khan, but that as soon as he finished, music blared out and people started to dance.
Khan's absence did nothing to dampen the festive spirits of the crowd, estimated by one police officer and a city official at between 25,000-30,000, outside parliament.
Songs were played from a large PA system in front of a sea of the red-and-green Pakistan Tehreek-e-Insaf flags being waved by young men and women.
"I miss Imran Khan and wish he could be at this wonderful rally. I don't think his absence will dampen, but rather boost our morale," said 21-year-old student Hassan Ali.
Although he has run an electrifying campaign, a question mark hangs over how well Khan will do, considering he won only one seat in 2002. He boycotted polls in 2008.
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