Eufemiano Fuentes, who is on trial for allegedly running a doping network in cycling, says he may be willing to name his clients in football.
Doctor Fuentes, who faces up to two-and-a-half years in jail on public health charges, has already claimed in his Madrid trial that he has clients in football, athletics, tennis and boxing.
It remains to be seen what impact Fuentes' potentially explosive information will have on other sports, if it can be corroborated.
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."
Fuentes denied he was orchestrate a plea bargain in a trial which has been under way since January.
Doping issues have been known in cycling for decades though the sport now considers itself to be clean, but testing in football is limited.
World Anti-Doping Agency (WADA) president John Fahey has slammed football authorities for not investigating the use of banned blood-booster EPO.
WADA has so far not been given access to the identity of blood bags seized by Spanish authorities, who want to keep the trial focused on cycling.
The five defendants on trial in the case will have a final opportunity to address the court on April 2 before sentencing commences.