Two men allegedly chased down a car, smashed the vehicle with an iron bar and then stabbed the driver in a horrifying attack.
The drama is reported to have unfolded close to the Carrfield Medical Centre in Heeley this morning.
A patient at the centre said: "Two men chased down a red Kia and started smashing the car with an iron bar.
"They then got the driver and started attacking him."
She added police attended the centre asking for witnesses and officers revealed it is believed a person was stabbed.
South Yorkshire Police has not yet released any details about the alleged attack.
The force has been contacted for comment and we are awaiting a reply.