The Sunday Age can reveal the ''non-presence'' line ASADA is taking after viewing one of the 34 show-cause notices that was issued to current and past Essendon players on Thursday.

In taking this route, ASADA has chosen the same non-analytical approach that its American equivalent, USADA, used to ban Armstrong from all sanctioned sports competition for life without relying on positive drug tests.

Proof of breaches by the 34 Essendon players could result in a two-year ban at most, or a six-month ban with mitigation.

ASADA's approach indicates it is confident about the supplementary evidence it has gathered over the past 16 months to mount the case that 34 Essendon players used prohibited drugs during 2012.

The notice seen by The Sunday Age relates to prohibited substance ''use'' and lists one allegation of ''possible non-presence anti-doping rule violation''. The only prohibited substance listed in this show cause notice is Thymosin Beta 4.

The notice refers to information the footballer gave in an interview to ASADA investigators early in last year's AFL season and states that the dates of the footballer's ''alleged attempted use'' was ''between about January 2012 and September 2012''.

The show-cause document, signed by ASADA CEO Ben McDevitt, states that Thymosin Beta 4 is ''prohibited under the S2 category of the World Anti-Doping Agency's prohibited list 2012''.

The S2 categorisation - outlined in WADA's international code, to which the AFL is a signatory - typically triggers an automatic two-year ban for athletes provided the doping rule breach is proved.

An excerpt of the notice seen by The Sunday Age states:

''After reviewing the evidence in this matter I have determined it is possible that you have used the prohibited substance Thymosin Beta 4 during the period between about January 2012 and September 2012.

''Specifically, it is alleged that you used Thymosin Beta 4 through your participation in an injection regime organised by Mr Stephen Dank and conducted in his office at the Essendon Football Club premises.

''Your actions may constitute a possible violation of clause 2.01 (2) (b) of the National Anti-Doping (NAD) scheme established by the Australian Sports Anti-Doping Authority Act 2006.''

Significantly, as revealed by Fairfax Media last week, ASADA engaged pre-eminent US-based litigation and sports anti-doping lawyer Richard Young to help build its cases around AFL players.

It's understood Young, who was a principal draftsman for the original WADA code and assisted USADA in its actions against cyclist Armstrong and sprinter Marion Jones, travelled to Australia more than once to assist ASADA with its probes into the AFL and NRL.

In an interview with Fairfax Media last week, former WADA president John Fahey suggested that Young's expertise was critical to ASADA's work regarding the investigation.

Assuming it has no positive drug tests from Essendon players to rely on, ASADA would no doubt have used Young to test the body of evidence it has gathered through interviews, witness statements and a vast number of documents.

USADA used the same primary method to strip seven-time Tour de France champion Armstrong of his titles and, in 2012, ban him from sport for life.

Provided the cases against Essendon footballers proceed beyond the show-cause notice stage, the allegations against the players would be prosecuted and heard under the AFL Anti-Doping Code, amended in March this year.

The AFL Anti-Doping Code includes important footnotes related to ''use or attempted use of a prohibited substance''. Footnote nine states, in part:

''It has always been the case that use or attempted use of a prohibited substance or prohibited method may be established by any reliable means … such as admissions by the player, witness statements, documentary evidence, conclusions drawn from longitudinal profiling, or other analytical information which does not otherwise satisfy all the requirements to establish 'presence' of a prohibited substance under clause 10(a).''

Essendon players and their legal advisers have 10 days to respond to their show-cause notices, although it's understood the AFL Players Association, which is co-ordinating the footballers' legal representation, is considering applying for an extension.

The day after the notices were issued, ASADA CEO Ben McDevitt urged the 34 AFL players served with notices to date to ''fully cooperate'' with ASADA. McDevitt indicated this could potentially help players have possible two-year bans reduced to six months.

''If an athlete can demonstrate, for example, that they didn't know what they were receiving was in fact a performance-enhancing substance, which was prohibited, then they may be able to claim no significant fault - which could lead to a reduction of up to 50 per cent in the penalty that could be imposed,'' McDevitt said on Friday.

''It may well be the case that an athlete doesn't know that they have actually received, through injection or ingestion or otherwise, the prohibited substance.''

He also said if players ''provided substantial assistance'', including making full admissions, they could be eligible to have potential doping bans reduced by a further six months - making a 75 per cent discount on a two-year ban starting point possible for Essendon players accused of taking Thymosin Beta 4.

McDevitt's public advice to Essendon players triggered a rebuke from Bombers chairman Paul Little. Essendon and its suspended senior coach James Hird have filed proceedings in the Australian Federal Court to challenge the validity of the joint AFL-ASADA investigation. If successful, the club and outcast coach believe the entire investigation could be extinguished.

When the AFL imposed unprecedented sanctions on Essendon last August for governance failings - this resulted in the club's removal from the finals series and Hird accepting a 12-month suspension - it referenced a document of more than 400-pages prepared with ASADA.

While ASADA subsequently continued its probe - and re-interviewed some central figures in the AFL investigation - that document referenced more than 13,000 documents, including transcripts of interviews with more than 130 witnesses.