Video report by ITV News correspondent Richard Pallot
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) has outlined.
The AAIB said the gas can "reduce or inhibit a pilot’s ability to fly an aircraft depending on the level of that exposure".
The report added it was working with the aircraft and engine manufacturers and the National Transportation Safety Board in the US "to identify possible pathways through which CO might enter the cabin of this type of aircraft.
"Work is also continuing to investigate pertinent operational, technical, organisational and human factors which might have contributed to the accident."
Piston engine aircraft such as the Piper Malibu involved in the crash produce high levels of carbon monoxide, the report said.
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.
A spokesman for Cardiff City said the club was "concerned" at the AAIB's latest report as it "once again highlights that the aircraft used for Emiliano Sala was not appropriate".
He added that "those who were instrumental in arranging its usage" should be held to account.
Several devices are available to alert pilots over the presence of carbon monoxide.
The AAIB said they are not mandatory but can "alert pilots or passengers to a potentially deadly threat".
What happened to Emiliano Sala?
Mr Ibbotson, 59, of Crowle, Lincolnshire flew Sala from Cardiff to Nantes in a Piper Malibu aircraft after he signed for the Welsh club.
The return flight – which crashed in the Channel – was on January 21.
Sala's body was recovered on February 6 and a post-mortem examination took place at Bournemouth Mortuary the following day.
The body of Mr Ibbotson has not been found.
Two people have been charged after accessing CCTV images of the post-mortem.