The Algerian defender has been sidelined since last November, having torn his anterior cruciate ligament. He did return to training, but only to fracture a kneecap during a February session.
Radio CRC are reporting that there are real fears over the 27-year-old fracturing the same kneecap.
The Naples side are said to have spoken to the Villa Stuart clinic and Professor Pier Paolo Mariani. The latest tests sent over to Mariani are understood to have worried the doctor, but he plans to visit the player and assess him physically before making a diagnosis.
Sources claim that Ghoulam took advice from an NBA specialist over that of his trainer, and the resulting exercises caused his knee to swell up.
With Napoli hoping to have the player ready for next season or sell him to a reportedly interested Manchester United, this comes as a heavy disappointment. The club, though, will have to wait on Mariani's checks to know for sure.
Ghoulam has made 153 appearances for Gli Azzurri since joining the club from St Etienne in 2014, scoring twice.