Khan, who as head of Pakistan Tehreek-e-Insaf (PTI) has electrified the campaign with calls for change, suffered fractured vertebrae and a broken rib on Tuesday when he fell from a lift taking him to the stage at a rally.
"It is impossible," Khwaja Nazir, a spokesman for the Shaukat Khanum hospital told AFP when asked if Khan would visit his constituency to vote on Saturday.
"His doctors are not allowing him to move out of the hospital, though he wants to move around," Nazir said.
PTI spokeswoman Shireen Mazari told AFP: "I don't think he will be physically able to go and poll his vote, and the date for postal ballot has expired."
"His health and safety is more important than anything else. He has to be stable first because at the moment he is not even walking."
Doctors expect Khan to make a full recovery, but have not yet specified how long he will need to remain in hospital.
"In the next two days, we will be in a better position to inform you about how many more days we will need to keep him in hospital. But his recovery is much faster than expectations," Doctor Faisal Sultan told reporters.
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