The Australian Transport Safety Bureau said on Thursday that a misaligned component had thinned the wall of an oil pipe in the exploded engine, causing "fatigue cracking" that prompted leakage and a fire "central to the engine failure".
"This condition could lead to an elevated risk of fatigue crack initiation and growth, oil leakage and potential catastrophic engine failure from a resulting oil fire," the ATSB said, noting it was "understood to be related to the manufacturing process."
The ATSB issued a directive urging Rolls-Royce to address the safety issue and take actions necessary to ensure the safety of flight operations in planes equipped with Rolls-Royce Trent 900 engines.
Qantas said it would immediately conduct further engine investigations as a result of the findings, but stressed it was just a precautionary measure and "there is no immediate risk to flight safety."
The carrier also said it has begun court proceedings to allow it to pursue legal action against Rolls-Royce ""if a commercial settlement is not possible."
"Today's action allows Qantas to keep all options available to the company to recover losses, as a result of the grounding of the A380 fleet and the operational constraints currently imposed on A380 services," the airline said.
Qantas grounded all six of its Airbus superjumbos after the November 4 blast over the Indonesian island of Batam, which forced an A380 to return to Singapore airport trailing smoke.
Flights were resumed last week, though the superjumbo has been barred from trans-Pacific trips to Los Angeles due to the extra engine thrust required.
Qantas said it would determine whether further action would need to be taken after inspections were complete and it had consulted both Rolls-Royce and regulators.