Demetriou was adamant that confirmation of only two investigations from the Australian Crime Commission and anti-doping authorities are under way through the AFL and would not overshadow the summer series start.
The league has confirmed that a full investigation is under way into allegations of multiple uses from Essendon players as well as one other player from an undisclosed club.
Demetriou was belligerent that performance enhancing drug use is not widespread in the AFL.
"We understand the concern, people, our supporters, our corporate partners and others would have on this issue," he said.
"To the best of our knowledge there's only two clubs involved with performance enhancing drugs, you know who one of them is and you that there is one player at one club.
"I want to stress to all our supporters, whether it's the NAB Cup or the AFL premiership season, to come along and watch their football.
"Have faith in the game a come along and watch your team.
"Because this is not a widespread problem relating to perforance enhancing drugs in our code."
Demetriou did concede that by withholding the name of another player club from another club had potential to taint all footballers during the six-week NAB Cup series.
“Up until the point in time that we’ve now been able to clarify that it’s one player, I think it had the potential to taint all players,” the league boss said at an animated media conference in Melbourne to launch the NAB competition.
“That’s why we sought urgently clarification and permission from the ACC on Friday night to make sure we got it out there so that we could specifically say to the public what this relates to when it comes to performance enhancing drugs.”
Demetriou conceded that the unknown player under ACC and Australian Sports Anti-Doping Authority investigation could play in the NAB series.
But the league boss constantly reiterated needs for the investigation to run a full course.
“There is that chance, but in normal circumstances if a player had tested positive to performance enhancing drugs, ASADA would be conducting an investigation in private, confidentially,” Demetriou said.
“We (AFL) wouldn’t know about it and then there is the potential that a player would be playing in that situation.
"If they are found to be guilty of taking performance enhaning drugs, they will be dealt with under the WADA code."