It happened on May 1 at a building on Third Avenue and East 167th Street.
Police say the suspect approach the 71-year-old victim from behind and beat him in the face with an unknown object until he was unconscious.
The suspect then took off.
The victim suffered a swollen eye and cuts to his face. He was taken to Lincoln Hospital for treatment.
Anyone with any information is asked to call NYPD’s Crime Stoppers hotline at 1-800-577-TIPS (8477) or 1-888-57-PISTA (74782) for Spanish. You can also submit a tip via the Crime Stoppers website, by Tweeting @NYPDTips or by texting a tip to 274637 (CRIMES) and then entering TIP577.