The 60-year-old Khan fractured a vertebra in his neck and two more in his back, Dr Faisal Sultan, a doctor at Shaukat Khanum Hospital, told a news conference this afternoon.
Khan also cracked a rib and cut his scalp, but reports that he had fractured his skull were incorrect, Sultan said.
"The spinal canal is intact and Imran Khan is in full control of all his limbs and his body functions," Sultan said.
The cricketer-turned-politician tumbled off a forklift that was raising him and three bodyguards to a stage in Lahore yesterday.
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He fell and sustained injuries to the back and head.
Doctors have advised Khan to rest in hospital for a few more days so that they can conduct further tests, Sultan said.
The injuries will knock Khan out of the last few days of campaigning before the May 11 general election though he may address one or two more campaign meetings by phone, leaders of his Pakistan Tehrik-e-Insaf party said.
Many analysts have tipped former premier Nawaz Sharif's as the front runner in the polls but Khan has made inroads in the most populous province of Punjab by wooing young and middle-class voters.