At about 9.15pm overnight, emergency services were called to Mary Ann Street in Ultimo.
They were told a 24-year-old man had been pushed from his delivery bike to the ground by an unknown man.
His attacker then stabbed him several times with a screwdriver.
The assailant, who remains unidentified, then walked away toward Wattle Street.
The delivery rider was taken to hospital in a serious but stable condition.
Anybody with information is urged to contact Crime Stoppers on 1800 333 000.