It happened just before 11 p.m. outside the Fuego Tipico Restaurant on East 188th Street in the Fordham Heights.
Surveillance video shows the 52-year-old victim, Jesus Cortez, exiting the restaurant and engaging a group of men and women.
Another man is then seen putting on a pair of gloves before sucker punching the victim, knocking him to the ground, unconscious and unresponsive.
The suspect then said something to the group before going back into the restaurant and eventually leaving the scene, police said.
The victim suffered a skull fracture, a broken cheekbone, and bleeding on his brain.
He was rushed to Jacobi Medical Center, where he remains in critical condition.
Cortez's niece, Anel Gomez, says the family feels helpless.
"We just got to wait, pray, and hope that everything goes well," she said. "When I saw the video, I was really shocked because I couldn't believe that someone just hit someone without saying something, without making any problems or trouble, because literally, my uncle was just standing there."
He was located at the hospital by his brother, who began looking for him after he didn't come home Friday night.
Police had responded to a report of an intoxicated man, and it was only when the brother reported to the hospital that they able to put pieces together and are now investigating the incident as an assault.
Investigators are looking to speak with anyone who was there at the time, including the people with whom the victim was speaking.
Since the victim was engaged in a conversation with the group, and then the suspect engaged in a conversation with the same group, it unknown at this time if the attack was random and unprovoked.
A suspect was arrested Wednesday morning, and 55-year-old Van Phu Bui is now charged with attempted murder.
According to state records, he is listed as a Level 3 sex offender on lifetime parole for the Christmas Eve rape of a 17-year-old girl in 1994.
The motive for the incident remains unclear.
Cortez's brother blinked back tears, telling reporters in Spanish that he was relieved to learn of the arrest. But the attack -- the single punch -- left Cortez with a devastating injury. The future, his brother said, is uncertain.
Anel Gomez says the family is taking it, day by day.
"Doctors are waiting for his brain pressure to go down to see if the hit caused any problem, like towards his body, or any brain damage," she said. "They don't know yet, because the pressure on the brain is really, really high."
Anyone with additional information is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782).
ALSO READ | NTSB preliminary report says pilot appeared sick, 'apologized' before exiting plane in mid-flight
NTSB preliminary report released for pilot who exited plane mid-flight
----------
* More Bronx news
* Send us a news tip
* Download the abc7NY app for breaking news alerts
* Follow us on YouTube
Submit a News Tip