THE AUSTRALIAN Sports Anti-Doping Authority has denied manipulating evidence in the Essendon supplements saga.

News Corp reported on Wednesday that the drug Thymosin Beta-4, which was administered to Essendon players ahead of their AFL suspension in 2016, was only listed as a banned substance several months after the injections to players had stopped.

But ASADA said the timing of the logging of the drug on its former checking tool known as 'Check Your Substance' was irrelevant.

Former captain Jobe Watson speaking in 2016 ahead of his return to the game. Picture: Michael Willson

"ASADA strongly denies allegations of evidence manipulation reported in the media," the organisation said in a statement.

"The World Anti-Doping Agency (WADA) has sole responsibility for setting and determining prohibited substances. It is not possible to manipulate whether or not substances are prohibited.

Essendon players training at St Bernard's College in 2016 ahead of their return. Picture AFL Photos

"Thymosin Beta 4 was included on the 2010 prohibited list by WADA … Thymosin Beta 4 has never been approved for human use.

"Whether a substance was on ASADA's former 'Check Your Substances' tool has no bearing on its status as a prohibited substance on WADA's prohibited list.

An emotional James Hird in 2015 on the day he announced he was standing down. Picture: AFL Photos

"It is impossible to list every substance that may be used for performance enhancement in such a tool, particularly those not approved for use by humans.

"In 2011-2013, for this reason, any person who searched for a substance on the ASADA website that was not contained in the 'Check Your Substance' tool would have received the following instruction: IMPORTANT: If you cannot find your search term on 'Check Your Substances' that does NOT mean that it is permitted in sport. Please check the list below for an exact match to your search term. If you cannot find an exact match for your search, please contact ASADA immediately."

There were 34 Bombers players who were banned for 12 months after a Court of Arbitration for Sport ruled the players were injected several times with Thymosin Beta-4.

The AFL has backed ASADA's handling of the matter.