Essendon's hopes of avoiding suspensions for players found to have taken banned substances rest on convincing the World Anti-Doping Agency that the club deliberately misled and ultimately betrayed its players.

As the drugs-in-sport inquiry enters its fifth month, Fairfax Media has learnt that its seemingly slow pace can be largely attributed to Essendon players being given every opportunity to build a no-fault or mitigating-circumstances case that will meet WADA's high evidentiary requirements.

Together: Essendon coach James Hird says his players have remained a tight group. Credit:Getty Images

Central to any no-fault or mitigating-circumstances case will be allegations players were duped into taking substances that they believed were WADA-approved and had been authorised by senior Essendon personnel, including the club's medical staff.

Investigators from the Australian Sports Anti-Doping Authority are examining whether players were given substances different to what they were told. There is also confusion over whether club medical staff had actually approved every substance administered.