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.

Essendon coach James Hird. Credit:Getty Images

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.