(CNN) Argentine footballer Emiliano Sala and his pilot were exposed to high levels of carbon monoxide inside the cockpit of their plane before it crashed into the English Channel in January, investigators say.

Sala and David Ibbotson were traveling from Nantes, France, to Cardiff, Wales, when their Piper Malibu aircraft crashed, killing them both.

The 28-year-old had joined the Welsh club for a reported £15 million ($19.3 million) from the French side and was heading to Wales after saying farewell to his former teammates.

Ibbotson's body has still not been found, but toxicology tests on Sala showed harmful levels of carbon monoxide in his blood, which could have caused a seizure, unconsciousness or a heart attack.

The report released by the Air Accidents Investigations Branch (AAIB) said it was likely that Ibbotson would also have been exposed to carbon monoxide.

Read More