The incident was reported around 2 p.m. Thursday inside the park on East 17th Street and Union Square West.
The victim was in the park at the time of the assault.
Authorities say the suspect and the victim did not know each other.
The man in question punched the 45-year-old victim in the face and made anti-gay statements, police said.
The victim suffered pain and bruising to the mouth as a result.
Anyone with 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).
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