The attack was reported around 11:40 p.m. in the 200 block of Columbus Avenue.
The 64-year-old man got into an argument with the suspect, who threw the victim into the street, causing him to hit his head on the pavement, according to police.
The suspect, described as a man in his 30s, fled on foot and had not been found as of this morning, police said.
The victim was taken to a hospital to be treated for his injuries, which are considered life-threatening, according to police.
Anyone with information about the case is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or to send a tip by text message to TIP411.