AFL chief executive Andrew Demetriou has accused some clubs of engaging in "scurrilous innuendo" to explain Essendon's unbeaten start to the season.
As an investigation into the Bombers and former sports scientist Stephen Dank continues, Demetriou said he knew for a "fact" that rival clubs were guilty of suggesting the possible use of illegal supplements in 2012 was having a residual beneficial impact on the team this season.
The Bombers have not conceded their players took non-approved peptides, including the anti-obesity drug AOD-9604.
"What I would say is this: there appears to be a small group, particularly amongst our clubs, who are taking it upon themselves to put about scurrilous innuendo about the fact the Essendon Football Club have won five games and are they getting an advantage," Demetriou said.
"I think this is really unfortunate. I think it's a byproduct of this running commentary and I don't think it is acceptable. It just might be that they have some good players, it just might be that they have some good tactics, it just might be that their coach is coaching well, they could just be playing well.
"The sooner some of our clubs, not all, but a small few, stop this sort of scurrilous mongering, the better. Because it's not doing anybody any good at all."
Demetriou said the Bombers were not "running away" from a joint investigation by the Australian Sports Anti-Doping Authority and the AFL.
"What I would say is they should focus on their own club. There are investigations ongoing at the moment with the Essendon Football Club," he said on 3AW.
"I remind people, they are fully co-operating. They came forward. They are not running away. They are part of this and they know it's going to take a while and we need to let it run its course."
The Bombers have shown class and a determination which has surprised many to win all five matches to start the season, and are likely to claim their sixth, against the winless Greater Western Sydney at Etihad Stadium on Saturday.
Essendon coach James Hird and several of his assistants have already been interviewed by ASADA and the AFL.
The players will begin their interviews next week, having already been briefed by lawyers Brett Murphy and Bernie Shinners from the AFL Players Association.
Captain Jobe Watson and the leadership group are set to be the first interviewed.
In a statement released this week, Essendon chairman David Evans said: "I want to repeat, our club has not conceded that our players have been given banned substances in 2012."
The Bombers' internal report, by former Telstra boss Ziggy Switkowski, will be released shortly. It had been due to be publicly unveiled on Wednesday but the club issued a statement confirming "a legal issue has arisen at the last minute, and the club is not able to proceed until this is sorted out".
Fairfax Media reported that a legal threat from suspended high performance coach Dean Robinson was the cause of the delay. The AFL has already seen a copy of the report.