The company had identified a leak on the line between an Osprey wellhead and the manifold earlier this month which divers successfully isolated last week.
However, a remotely operated vehicle, which was mobilised on Wednesday to assist in monitoring start-up operations, identified another “significantly smaller” leak on a different part of the manifold.
Fairfield said it would take “some time” to source the equipment needed to carry out the new repairs and as a result the Osprey manifold and its associated pipework would be filled with water.
It added the two Osprey wells would also remain shut-in until the repairs had been carried out.
The UK Department of Energy & Climate Change (DECC) said in an earlier release on Wednesday that Fairfield had notified it that roughly a further 1.5 barrels of oil had been leaked between 20 July and 24 July.
As of 25 July it was estimated the total volume of oil released to sea since the first leak was originally identified was almost 89 barrels of oil.
“Fairfield have provided DECC with an Environmental Impact Assessment which confirms the oil released to sea will have minimal environmental impact,” the department said in its statement.
Osprey is a a multi well subsea development that feeds back to the Fairfield-owned Dunlin Alpha installation about 195 kilometres north-east of Shetland.