Police responded at 11:39 p.m. to 101 Market St. for what appeared to be a stabbing that left the victim with one cut to his neck, police said.
The victim and a man started arguing over an undisclosed issue, police said. The suspect then pulled a knife and stabbed the victim once on his neck.
The suspect, described as anywhere from 30 to 40 years old, fled on foot after the attack, police said.
The victim was taken to San Francisco General Hospital with injuries not considered life-threatening, police said.
The suspect was described as a white main standing about 5 feet 11 inches with a thin build, police said.
The stabbing is under investigation by the department's Criminal Investigations Unit.
No arrests have been made, police said.
The stabbing happened on the sidewalk in front of the Federal Reserve Bank of San Francisco, where "reoccupiers" from Occupy SF have been camping since last month, according to the group's website.
A stabbing Sunday night at the same location left a 28-year-old man in critical condition, according to San Francisco police.
The suspect in Sunday's stabbing is described as a white man between 20 and 25 years old who is about 5 feet 5 inches tall, weighs about 135 pounds and has blond hair and blue eyes. He was last seen wearing a dark-colored beanie, a dark-colored puffy jacket and black-framed glasses, police said.
Police are continuing to investigate the stabbings. Anyone with information about the case is encouraged to call the anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.