Off-site injections given to Essendon players will reportedly be at the centre of the AFL's investigation into possible inappropriate use of substances by the club's sports science staff.

As the fallout from the investigation begins, News Ltd is reporting Bombers players were taken to off-site locations and injected with unknown supplements during last season.

It comes as two other clubs, Geelong and Gold Coast Suns, said they would assist the investigation after confirming they previously employed individuals involved with the Bombers' fitness program.

On Tuesday, Essendon confirmed they had asked the AFL and the Australian Sports Anti-Doping Authority to launch an investigation after the club discovered "concerning" information about supplements taken by their players.

ASADA's regulations mirror those of the World Anti-Doping Authority (WADA), where players and officials can face up to a two-year ban for a first offence.

Former Essendon player Kyle Reimers said the club knew they were pushing the boundaries when they took supplements last year.

Reimers, who was delisted by the club at the end of last year, told Channel Nine that players were asked to sign waivers taking responsibility for supplement use.

"They admitted to it, it was right on the edge," he said.

"Speaking to blokes from other clubs, I don't think anyone's ever thought about signing it or doing the stuff we were doing.

"After a few months away from it ... it does seem very odd the type of stuff we were taking."

Essendon have also reportedly suspended high-performance manager Dean Robinson pending the inquiry.

Robinson, nicknamed 'The Weapon', came under fire last year when the Bombers suffered a staggering run of soft-tissue injuries.

The former Geelong employee joined the Bombers in 2011 and recruited sports scientist Stephen Dank, known as 'The Pharmacist', to assist with Essendon's new training program.

Dank, who was sacked by the Bombers last year, had previously worked at the Suns and NRL club Manly. Manly have released a statement saying they complied with all anti-doping regulations during Dank's time at the club.

AFL boss Andrew Demetriou said it would be premature to comment on any possible sanctions and urged people to "not jump to conclusions".

However, he said ignorance about the legality of substances is not an excuse.

"Under the ASADA rules, whether you knew or not it's no excuse ... they are the WADA rules," Demetriou said.

"Under the rules, the way they are structured at the moment, which all world sport has to follow, they apply to officials and under our rules they can apply to a club.

"In relation to WADA, when it comes to rules, and the rules are pretty specific, and other people have abused them ... but these guys get educated every year and they know before they ingest anything or take anything, and if you have any doubt, you ring the hotline or ring your doctor."

While supporting the investigation, the AFL Players' Association (AFLPA) indicated the club should take responsibility for substances given to their players.

"Clubs providing players with supplements and directions as to their players' training requirements have a significant responsibility and in our view, any concerns regarding the nature of such directions ought to be treated with the utmost seriousness," AFLPA chief executive Matt Finnis said.

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