Imran Khan has fractured his skull and required hospital treatment after he fell from a fork-lift truck that was carrying him on to the stage at a packed rally.
The 60-year-old leader of the Pakistan Tehrik-e-Insaf party fell up to 15ft (4.5m) from the fork-lift as he was being transported with two guards.
Television footage showed the former cricketer-turned-politician being carried away by supporters and being bundled into a vehicle before being taken to hospital in Lahore.
As hundreds of people gathered outside the hospital, Ijaz Chaudhry, an official with Mr Khan's party, told the Associated Press that the former sportsman's injuries were not life-threatening and that he had not lost consciousness.
Later, Mohammed Shafiq, the doctor who attended him said that Mr Khan received seven stitches for a six-inch long wound in the head. He said the cut was not deep.
"He is fully conscious and he was complaining of backache. He is fine, but he must have some rest for one or two days," Dr Shafiq added in comments broadcast on Pakistan's Geo News. Party leaders are set to meet today to discuss how to continue his campaign over the next three days.
Meanwhile, three bombings in north-west Pakistan targeting individuals involved in this weekend's election killed 18 people.
Two of the attacks targeted candidates from Islamist parties, indicating a new trend ahead of the country's election on May 11, which had only plagued secular parties before this week.
The death toll from attacks on candidates and party workers since the beginning of April now stands at more than 100.
In the deadlier of the three attacks, a suicide bomber on a motorcycle detonated his explosives near a vehicle carrying a candidate from a hardline Islamist party, killing 12 people and wounding 35, police said. It was the second attack on the Jamiat Ulema-e-Islam party in as many days.
In the village of Babagam in Khyber Pakhtunkwa, a roadside bomb hit a vehicle carrying a local leader of the Pakistan People's Party. The blast killed the leader, Zahir Shah, along with two of his guards and two supporters. Mr Shah was in the area campaigning for his brother.
The Pakistani Taliban claimed responsibility for the attack in a phone call to the Associated Press.
Mobile phone footage