Spanish doctor Eufemiano Fuentes, who is on trial for allegedly running a doping network in cycling, has said that he would be willing to name his clients.
The medical expert, who faces up to two-and-a-half years in jail on public health charges, had already revealed in his Madrid trial that he has clients in football, athletics, tennis and boxing.
However, the revelations on Wednesday that he might give the information to doping authorities could have a huge impact on the footballing landscape if major players, teams or organisations are involved.
Fuentes told reporters attending the trial: "If they [anti-doping authorities] believe that I am useful and they ask me [to co-operate] I would consider it and I would be ready.
"What I don't know is if what I could contribute would be worth anything to them or not.
"This would be in exchange for mutual collaboration. If the list was necessary within this collaboration, they would get it."
The doctor denied he was trying to hint at a plea bargain in a trial which has been under way since January, when quotes first emerged from Fuentes confirming he had footballing clients.
Doping issues have been known in cycling for decades though the sport now considers itself to be clean, but drug bans in football are uncommon.
The likes of Cristiano Ronaldo and Vicente del Bosque have claimed that it is a problem that the sport has avoided, but World Anti-Doping Agency (Wada) president John Fahey slammed footballing authorities for not investigating the use of banned blood-booster EPO.
Wada has so far failed to be given access to the identity of blood bags seized by Spanish authorities, who are intent on focussing the trial on cycling.
The five defendants - including Fuentes' sister, Yolanda - will have one final opportunity to address the court on April 2 before the trial is set to come to a conclusion.