Emiliano Sala was exposed to high levels of carbon monoxide prior to a fatal plane crash in the English Channel.
Sala signed for Cardiff City two days before the crash.
Sala, 28, and pilot David Ibbotson, 59, crashed on 21 January while travelling from Nantes in France to Cardiff.
Toxicology tests on Sala's body showed carbon monoxide levels in his blood were so great it could have caused a seizure, unconsciousness or a heart attack.
The Sala family says there should be a detailed examination of the plane.
Piston engine aircraft such as the Piper Malibu involved in the crash produce high levels of carbon monoxide.
The gas is normally conveyed away from the aircraft through the exhaust system, but poor sealing or leaks into the heating and ventilation system can enable it to enter the cabin.
[Source:BBC Sports]
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