Witness Raza Zaidi said Khan was being lifted on a crane with five people but lost his balance and fell when a sixth one tried to climb up. Khan hit the lifter before falling on the ground.
The rally was held near Ghalib Market in Lahore's Gulberg neighbourhood. Doctors said that he is out of danger.
In the meantime, political violence continued in Pakistan with the death toll exceeding over 200 since the campaigning started in the country last month with the Tehreek-e-Taliban Pakistan widening the net of those it is targeting, including the right-wing Jamiat-e-Ulema-Islam Fazlur Rehman faction in its attacks.
On Tuesday, a blast during an election campaign of the JUI-F killed at least 11 people in Hangu. A roadside blast on the same day during a Pakistan People's Party rally killed six in Lower Dir.
(With inputs from AFP)