Officers responded to The Embarcadero and Broadway at about 12:30 a.m. where they found the man, who is in his 30s, injured from multiple stab wounds all over his body, San Francisco police Officer Albie Esparza said.
He was transported to San Francisco General Hospital in serious condition, though he is expected to survive, Esparza said.
The man had been riding his bike when he was approached by three male suspects who then punched and stabbed him apparently out of the blue, according to Esparza.
"They just confronted him and began to punch and stab him multiple times," Esparza said.
He said the suspects didn't take the man's bicycle or any of his other property.
The three suspects had not been arrested as of 10 a.m.