A dispute over crucial anti-doping evidence which the 34 past and present Essendon players facing bans say has been denied to them by ASADA is expected to be resolved at a directions hearing early on Monday.

Fairfax Media understands a significant amount of that evidence was forwarded on Friday to the players' lawyers, with the players increasingly frustrated at ASADA's refusal to provide them with witness statements and other detail which has been gathered by the anti-doping investigation.

The move came as genuine doubt emerged over whether key witnesses in the case against the players - Shane Charter and Nima Alavi - would agree to appear before the AFL's anti-doping tribunal. It is believed a series of requests from ASADA to both Charter and Alavi have failed to secure their presence as witnesses in the hearing, which is due to start on December 15.

And former Essendon high performance manager Dean Robinson has also not yet agreed to give evidence on behalf of the players. Robinson, who received a $1 million settlement from Essendon in late September, has just returned from abroad and is expected to make his decision over the coming days.

Charter, the so-called anti-ageing clinician and former body builder, is alleged to have sourced the banned drug Thymosin beta-4 which was later given to disgraced Stephen Dank. Dank told Fairfax Media he had given the players the drug, however changed his version of events after learning that it was banned under the world anti-doping code.