Khan, whose political party is expected to be a major force in parliamentary elections scheduled for Saturday, was standing on the platform with several other people when they fell about 15 to 20 feet.
Local television video showed the bloodied politician being carried away by supporters. Waleed Iqbal, a leader of Khan's Movement for Justice party, later said Khan was conscious and in stable condition at a Lahore hospital.
Iqbal said Khan wanted to return to the Lahore rally but his doctors advised him against doing so. Another top aide, Asad Umar, said Khan got several stitches but was "in high spirits."
Khan later spoke to reporters from his hospital bed, urging people to vote for his party.
"I have done whatever I could do," he told national broadcaster Dunya TV, according to the Associated Press. "Now you have to decide whether you want to make a new Pakistan."
Campaigning for Saturday’s poll has been marred by a wave of attacks. On Tuesday, two bomb blasts killed at least 15 people and injured more than 40 at rallies in northwestern