Toxicology reports say that Emiliano Sala had a high saturation level of the combination product of carbon monoxide and haemoglobin in his system according to the Air Accidents Investigation Branch
The Argentinian star had signed a 15 million pound contract with Cardiff City and was flying to join the team when his plane crashed, killing the 28 year old and the pilot.
The AIB also says it is considered likely that the pilot David Ibbotson would also have been exposed to carbon monoxide.
It comes after the branch published a second Special Bulletin on the loss of Piper Malibu aircraft.
This Special Bulletin highlights the danger of exposure to carbon monoxide in both piston and turbine engine aircraft.
A final report will be published when the investigation has concluded.