The injured man is understood to have been walking at Hollybank Road, near Intake, when the incident happened, and emergency services attended.
He was taken to hospital after the collision.
A spokesman for South Yorkshire Police said: “Officers were called at 5.25pm on Tuesday, December 21 to reports of a road traffic collision involving a pedestrian and a cyclist.
“The pedestrian suffered head injuries.”
It is not known if the cyclist was injured in the incident.
An ambulance was also called to the scene, shortly after the police were contacted.
A spokesman for the Yorkshire Ambulance Service said: “We received a call at 5.46pm on Tuesday (December 21) to reports of a pedestrian knocked over by a cyclist on Hollybank Drive, Intake.
"The police were in attendance and informed the ambulance service that the patient was being taken to hospital by a family member.”