The deputy chief of Navy does not expect it to be "safe or practical" to remove "absolutely all the liquids" from the HMNZS Manawanui.
Fuel removal from Manawanui is expected to start in December, a statement from the New Zealand Defence Force (NZDF) said.
It will be done by salvage companies Pacific 7 and Bay Underwater Services NZ.
The Navy vessel sank after running aground on a reef in Samoa last month.
Deputy Chief of Navy Andrew Brown said the first priority was to remove the "bulk fuel" first which poses the largest environmental risk and progressing to the smaller quantities of oils and other contaminants.
"In the end we do not expect it will be safe or practical to remove absolutely all the liquids, however the objective is to do everything practicable to limit or stop any potential damage to the environment," Brown said.
The operation to remove the fuel would be done as quickly and safely as possible, but this would be dependent on several factors, such as weather and sea conditions, he said.
A statement from the NZDF said the equipment needed for the fuel extraction is expected to leave New Zealand in the next week and should take about 10 days to arrive.
"It is important to emphasize that the NZDF's intent is to get the fuel and other pollutants off the vessel as soon as we can," Brown said.
"That needs to be done safely, with minimal risk to the personnel involved."
A final Court of Inquiry report into the sinking of the vessel is expected to be completed around the end of February and is due to be released to the public by late March after it has been subjected to legal review.