CEO Andrew Demetriou says the AFL does not know the identity of the single player being investigated for possible doping, and that the player could potentially play during the NAB Cup.
Multiple players from Essendon and one player from one other club are under investigation.
An animated Demetriou said the AFL was unable to notify the other club because the AFL itself did not have that information.
"I want to make it clear we have not been told the identity of the one player," Demetriou said.
"We're doing our very best to be transparent but this is a very special set of parameters sets upon us."
But he said that the club may have been notified already. "The ACC with their extraordinary coersive powers may have already spoken to that player, or that club. I don't know."
He said that if a player was being investigated by ASADA for performance-enhancing drug use, that investigation would be private, and the player could still be playing while being investigated.
"ASADA would be conducting an investigation in private, confidential, and we wouldnt know about it," he said.
He said that the AFL would be speaking to all clubs, because as far as the AFL was concerned, all clubs had "vulnerabilities" to illicit drugs. He also repeated his warning that organised crime was a major issue for sport internationally, but that he was relieved match-fixing was not currently an issue in the AFL.
"We are now able to speak to the clubs that are mentioned in the reports and in our briefings to notify them of the vulnerabilities they have to illicit drug use," he said.
Demetriou said that drugs were not a "widespread problem" in the AFL, but said that before the details of who was being investigated were released, it did have the potential to taint all players.
But in an interview with ABC1's 7.30 program, Stephen Dank, the sports scientist at the centre of the investigation into Essendon, said that it would be foolish to think that the Bombers were the only ones looking into programs to improve performance.
"I don't think, you know, you'd be sort of foolish to think that Essendon were the only that were looking at these sort of programs," Dank said.
"And I think when you think of what these players do on a week to week and a year to year basis, I think you've got 18 clubs that are all very well coached and obviously all have a very good high performance unit and they want cutting edge."
The interview will air on Monday night.
Earlier, the journalist who interviewed Dank for the program, Caro Meldrum-Hanna, said she found him to be ''an honest individual''.
Speaking on Triple M radio, Meldrum-Hanna said there would be ''revelations'' from the interview.
"You'll hear from what Dank has to say tonight that he's certainly of the view that what he has done is within the rules and regulations," Meldrum-Hanna said.
"I found Steven Dank to be, I certainly found during the interview which was a lengthy one, that he was an honest individual.
"He sat there and answered every question that I put to him, and some of these were certainly pretty hairy ones, and there was at no time where he was ever willing to call off the interview," she said.
"He sat there and endured a very long list of questions which started from his qualifications and his training right up to the time he left Essendon."
She said he did not hesitate in responding to all of the allegations against him.