Campbell, 42, was knocked down and robbed as she hailed a taxi about a month ago. She suffered a torn ligament in the incident, which wasn't reported by the media until Friday.
"It was terrifying. Naomi believes the assailant had been watching her, casing her out, and waited for a moment to strike when she was alone. She was attacked in the street as she hailed a cab, and robbed," a source told the Post.
"Her leg was injured as she was violently pushed to the ground. She was understandably very upset and shaken up."
The newspaper said it is unclear what was stolen.
Campbell is being treated by an orthopedic surgeon in Vail, Colo., for her injury, the Post said.
No arrests have been made in the case.