The man, aged in his 50s, was travelling along Minna Road, Burngreave, at 6.05am yesterday when his silver Vauxhall Astra struck a bollard and brick wall close to the junction with Burngreave Road.
His car then struck traffic lights at the pedestrian crossing outside the Premier Convenience Store close to Burngreave Street.
South Yorkshire Police said the motorist is believed to have suffered a medical episode at the wheel.
He was taken to hospital, where he remains this morning.
South Yorkshire Police said: “Officers are keen to speak to anyone who saw what happened and are asking anyone who has any information to contact them.
“If you can help, please call 101 or submit an online report quoting incident number 146 of March 30.”
Nobody else was injured in the incident.