Essendon coach James Hird has been revealed as the key witness who claimed that AFL boss Andrew Demetriou had spoken with Bombers chairman David Evans on the eve of the club's decision to self-report about his players' substance use.

Hird is understood to have told the ASADA-AFL investigation that Demetriou called Evans at his home on February 4 during an emergency meeting involving Evans, Hird, former CEO Ian Robson, club doctor Bruce Reid and football boss Danny Corcoran.

The Hird evidence, later corroborated by Corcoran, appears to place the Bombers coach at odds with his chairman, who has denied claims he was tipped off by Demetriou. Ian Robson has backed Evans' version of events.

It has also firmly placed the Hird camp at odds with Demetriou, who has repeatedly denied confirming to Evans that Essendon had an issue with potentially banned substances. Hird's evidence reportedly suggests Demetriou and Evans discussed the club's use of potentially banned substances.