Smith had just returned to his townhouse in a chauffeur-driven car when he was approached from behind by man who held a gun to Smith's head, Clifton police Capt. Robert Rowan said.
"He said to him, 'Give me everything you got,' and Mr. Smith turned over his jewelry and money and cell phone," Rowan said Tuesday.
The man left the scene and is still being sought, Rowan said. It was unclear if Smith's driver was at the townhouse during the holdup.
The robbery was first reported Sunday by NBC's Tiki Barber, a former Giants running back.
NFL security has been informed of the incident, league spokesman Greg Aiello said, according to Newsday. "We're aware of the situation," he said.
The Associated Press contributed to this report.