The officer, who is reported to have lost consciousness after the incident in Sheardown Street, off Hexthorpe Road, Hexthorpe, was rushed to hospital.
A police cordon is in place close to the Mark Jarvis bookmakers, with forensic experts in white suits examining the area.
Side streets off Hexthorpe Road have also been taped off, with officers guarding the crime scene.
Two men and a woman are reported to have been arrested over the incident.
Details have not yet been released by South Yorkshire Police.