Essendon has described the season-long suspensions handed to its players by the Court of Arbitration for Sport as "manifestly unfair".

The CAS found 34 past and present players guilty of taking banned substance Thymosin Beta-4, of whom 12 are still on the club's list.

"The penalty imposed on the 34 players is manifestly unfair," Chairman Lindsay Tanner said on Tuesday afternoon.

"At all times our players acted in good faith. They sought assurances and were provided them.

"If ever there was a case to be made for no significant fault (of the players), this was it." 

Tanner said the CAS findings were devastating for the players, particularly given the uncertainty during the three-year ordeal.

"The finding is heartbreaking for our players, who will struggle to understand how two tribunals could come to different conclusions based on the same evidence," he said.

"We felt that the comprehensive verdict of the AFL Anti-Doping Tribunal last year was the correct one.

"Notwithstanding that, we do acknowledge the authority of the Court of Arbitration for Sport and we must accept its decision."

Tanner, on behalf of the club, again apologised to the players and the club's supporters for "a mistake of the highest magnitude" in its decision to implement its controversial supplement program in 2012.