Essendon are under siege as they reel from potentially the biggest crisis in AFL history.

Security guards kept fans and media out of the Bombers’ new Tullamarine facility as the players trained on Wednesday morning, less than a day after the club became the subject of an anti-doping investigation.

The Australian Sports Anti-Doping Authority (ASADA) is joining with the AFL integrity unit to look into supplements that were given to Essendon players last year as part of their fitness regime.

If the investigation shows that players were given banned substances, the ramifications are massive.

“The jury is out on this at the moment,” former ASADA chairman Richard Ings told FoxSports.

“But if this substance does come back and it turned out to be a prohibited substance, (then) it’s a house of cards.

“This could be very serious for the players involved and extremely serious for the club.”

Tim Watson, the former Essendon captain and father of current Bombers captain Jobe, said he was angry when he learnt on Tuesday about the unfolding story.

He said regardless of what the investigation finds, his old club needed to look hard at its management.

“I was thinking about the gullibility of people who are in charge of a football club,” Watson told SEN.

“I understand the naivety of players because that’s why they are – they come into the system, they’re a bit like cattle, they get told this is what they need to do.

“If a supplement was there, of course they would be thinking `okay, if the club has given their sanction, then this is okay … there is nothing illegal or untoward’.

“I’m bewildered that this could possibly even take place in a modern-day, AFL, professional football club.

“It beggars belief, at face value, they have allowed what has been reported to occur.”

Watson was asked how he would feel if his son was caught up in the controversy and ended up losing last year’s Brownlow Medal.

“As a parent, I’d be devastated for him … you’d be completely and utterly destroyed,” Watson said.

“I’m angry, I’m frustrated as a former player and a parent.”

Sports scientist Stephen Dank, who once worked in the NRL, was at Essendon last season and has since left the club.

There are unconfirmed reports that the Bombers have also stood down fitness coach Dean Robinson.

The Bombers went to the AFL with their concerns about the supplements and the league referred the matter to ASADA.

Essendon say they only became aware of the potential problem this week, but rumours had been circulating for months.