Flammable methane gas continued to leak on Wednesday from the abandoned platform, 150 miles east of Aberdeen, as experts warned the gas cloud - just 120 yards from a flare which is still burning - was an "explosion waiting to happen".
Total admitted the gas could ignite but insisted there was only a "low" risk because the wind was blowing the gas cloud away from the flare.
Shares in Total, which lost nearly 6pc on Tuesday, fell again on Wednesday, wiping a further €1.2bn off the company's value, although they appeared to be buoyed slightly by Fitch saying it believed the unfolding incident was "not as serious as BP's Deepwater Horizon accident in 2010".
However, Fitch said it had not factored into its ratings "any catastrophic accident on the platform resulting in an explosion, or a dramatic worsening of the current situation". In a "worse-than-base-case" scenario, Fitch said, Total may have to shut down the Elgin field to stop the gas leak.
Were the field to become "permanently unusable", it said, based on third-party valuations "it would cost Total €2.6bn - its share in Elgin - and the company might have to compensate its partners for the remaining €3.1bn". Total said it was still considering drilling a relief well to stop the leak, an option that could take more than six months. Analysts at RBC Capital Markets said that the relief well could cost Total $200m.
John Shanks, of engineering consultancy RiserTec, said: "If gas continues to leak at a steady or increased rate over a sustained period of time, the platform could become an explosion waiting to happen."
David Hainsworth, Total's safety manager, said the flare was lit at the time the leak was discovered on Sunday as a deliberate safety measure to burn off high pressure gas from containers within the Elgin processing platform.
The gas had been burnt but small quantities of liquid were still evaporating from the storage vessels. The valves could not now be shut to stop the release but it should run out naturally, he said.
"We believe the flame is diminishing but there is a possibility it could carry on for several days. There is a risk of ignition if the wind changes and the plume is at the right concentration but our view is that is a low risk. The gas cloud is blowing away from the platform."