Footballer Emiliano Sala was exposed to harmful levels of carbon monoxide before he was killed in a plane crash and it is likely his pilot was also affected, accident investigators said.
Tests on the striker's body found enough evidence of the harmful gas to cause a heart attack, seizure or unconsciousness, an interim report by the Air Accidents Investigation Branch (AAIB) stated.
It is likely that pilot David Ibbotson was also "affected to some extent" by exposure to carbon monoxide, the document added.
The AAIB said the gas can "reduce or inhibit a pilot's ability to fly an aircraft depending on the level of that exposure".
Argentinian footballer Sala signed for Cardiff City from French club Nantes for £15 million on 18 January.
Mr Ibbotson, 59, of Crowle, Lincolnshire flew Sala from Cardiff to Nantes in a Piper Malibu aircraft the following day.
The return flight, which crashed in the English Channel, was on 21 January.