The finding came just two months after an engine cracked and failed during test aboard a Boeing 787 at Charleston International Airport, the Associated Press reported.
The FAA responded to that failure by ordering immediate inspections on General Electric engines that power the Dreamliner, adding that failure of a component in the engines could cause "possible loss of the airplane," according to KOMO News.
United Airlines is scheduled to begin flying the aircraft on US domestic routes in November.
The GEnx-1B turbofan engine found with a cracked mid-shaft was installed on a 787 that had not yet flown, according to the AP.
GEnx engines are manufactured at a General Electric facility in Cincinnati.
Reportedly a 747-8 cargo plane may also have been affected.
As a precaution, the NTSB — which investigates all US civil aviation accidents — on Friday called for frequent inspections on Dreamliner engines, CNN reported.
A similar General Electric engine on a different kind of aircraft — a Boeing 747 — lost power during takeoff at Shanghai Pudong International Airport on Sept. 11 last year, CNN reported.
The first Boeing 787 Dreamliner rolled out in 2011, three years late and billions of dollars over budget.
The NTSB, said its investigation into the latest engine troubles was continuing.