Duke Street was sealed off and an air ambulance was called after the incident at around 3.15pm.
Witness Christine Bentley assistant manager at Boyes said the collision happened after a van hit the man.
Christine said she helped put the man into the recovery position after he was knocked into the air by the van.
"I sat and talked to him. He was hardly breathing.”
The air ambulance is pictured landing on the roof of the Civic Quarter car park.
The air ambulance was seen taking to the air again from the grassy area near College Road.
A spokesman for Doncaster Police said: “Officers were called today (Friday 19 November) at about 3.20pm to report a collision between a van and a pedestrian on Duke Street in Doncaster.
“A man, aged in his 70s, suffered a head injury not thought to be life threatening and was transported to Doncaster Royal Infirmary.
“The van driver remained at the scene and enquiries are ongoing at this time.”