Essendon club officials have been unable to tell the Australian Sports Anti-Doping Authority or their players what drugs some of them were given when they were injected with a substance bought in Mexico by a Melbourne man suffering muscular dystrophy.
The revelation that some players were injected with an unknown substance purchased overseas and not intended for use by sportspeople has prompted health concerns from the relatives of some players.
ASADA has been unable to determine what was in the bottle bought in Mexico despite interviewing the chiropractor who provided it to Essendon players.
Investigators have also quizzed the players who were injected with the Mexican supplement at a South Yarra clinic and have interviewed Bombers staff, including coach James Hird.
The inability of the club to identify what its players were given when several were injected with the Mexican-sourced supplement is understood to be a key part of ASADA's interim report and an example of the inadequate supervision of Essendon's supplements program.
Essendon chairman Paul Little and Hird have this week
publicly asserted their belief players were not given any illegal or harmful drugs, although it is understood no one at Essendon can state with certainty what the Mexican supplement contained. A club spokesman on Wednesday declined to respond to questions about the Mexican supplement.
Even though Essendon, ASADA and the AFL are all uncertain about what was in the Mexican supplement, sports scientist Stephen Dank - who oversaw the supplements program - has previously stressed all drugs used at the South Yarra clinic were harmless, routine amino acids or peptides.
But his claim has not allayed concerns about the Mexican supplement inside the Bombers or the AFL. Insiders are questioning why Dank and clinic owner Mal Hooper would use a product from Mexico whose precise contents were unknown, given amino acid and peptide supplements can be sourced easily from reputable Australian pharmacists or health shops.
According to evidence gathered during the ASADA-AFL investigation, the Mexican supplement was left in the South Yarra hyperbaric chamber clinic owned by Hooper - a controversial chiropractor recently deregistered for providing unproven treatments to a cerebral palsy sufferer - by one of the clinic's patients who suffers from muscular dystrophy. The patient had purchased the supplement in Mexico.
Hooper's clinic promotes the health benefits of using certain amino acids and peptides while undergoing hyperbaric chamber therapy.
Hooper, an associate of Dank, treated Essendon players in his hyperbaric chamber during the 2012 season. In September 2012, club officials discovered Hooper and Dank had also given the players supplements at the South Yarra clinic after Hooper sent the club invoices for the provision of ''amino acids''.
The revelation that an unknown substance was given to some Essendon players was raised by ASADA investigators during interviews at AFL headquarters and with figures associated with Essendon's supplements program. The Mexican supplement is understood to have created angst among a small number of players or their relatives.
AFL Players Association boss Matt Finnis refused to comment on Wednesday but has previously said: ''I'm not surprised that players have been angry and concerned. I'm aware of the interviews and I've had my representatives and my lawyers at the meetings.
''Suffice to say we are aware of the matters that have been raised and we have never underplayed the seriousness of this inquiry.''
ASADA has devoted considerable resources to examining the circumstances around the provision of the Mexican supplement.
One witness who was interviewed by ASADA and who witnessed the Essendon players attending Hooper's clinic said that investigators had asked him whether the bottle in question might have contained something improper. The witness told ASADA he was unsure what was in the bottle, although he assumed it was amino acids.
Hooper has refused to publicly reveal what was in the Mexican bottle other than stating that nothing in it breached WADA's anti-doping code.