The confrontation happened Sunday afternoon on Emery Street in Hempstead.
The Nassau County officer was slashed across the stomach and left hand with a 5-inch knife during a struggle with 32-year-old Christopher Sargeant.
"As they tried to take the suspect into custody, the subject was still armed with a knife," Nassau County Deputy Inspector Kenneth Lack said. "The officer didn't even realize he was stabbed until the subject was on the trundle and they were bringing him upstairs. Then the officer told the other officers at the scene, 'I think I'm injured.'"
Sargeant is a former New York City Rikers Island correction officer who was fire last month due to a medical disability.
Police visited his home Sunday after a complaint that he was throwing rocks at cars.
Neighbors say the incident was out of character for Sargeant.
"I've known this guy my whole life," neighbor Nathaniel Sample said. "He taught me how to play basketball. I've known him my whole life, and he's never hurt nobody. None of that. Never been involved with no drugs, gangs, anything."
The name of the injured officer has not been released, but he is a 13-year veteran of the force and is 54 years old. He is expected to be released from the hospital sometime Monday.
Sargeant is facing multiple charges.
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