Ameobi suffered an injury on reserve team duty.
The 19-year-old limped off during Tuesday's second string victory over Wigan and could face a lengthy spell on the sidelines.
NUFC spokesman: "Sammy Ameobi will be sidelined for a period of time, likely to be a number of months, as a result of an injury sustained in the reserves' win over Wigan."
News of his injury will come as a huge blow to manager Alan Pardew, who already has defender Steven Taylor and midfielder Sylvain Marveaux on the long-term injured list.
However, with Hatem Ben Arfa now back fit and Danny Guthrie approaching a return, he at least has some positive news.