Alex Rodriguez says if he doped he was duped.

According to a source with knowledge of Rodriguez’s ongoing arbitration hearings the embattled Yankee and his lawyers have presented a case based partly on the idea that Rodriguez believed the substances he procured from the Biogenesis anti-aging clinic were innocent legal supplements.

That narrative conflicts with the version told by Anthony Bosch the founder and proprietor of the now-shuttered facility who spent part of Monday and almost all of Tuesday testifying before the three-person panel that will decide on the appropriateness of the 211-game doping ban Major League Baseball commissioner Bud Selig imposed upon Rodriguez in August.

Bosch who is cooperating with MLB has spent much of that time validating a vast trove of Biogenesis documents as well as his own electronic communications with Rodriguez. The league believes the evidence reflects a deep dealer-source relationship. If the Biogenesis products were legitimate MLB argues why were they so expensive and why were the transactions so secretive?

Attorneys for Rodriguez will likely begin their cross-examination of Bosch on Wednesday attacking his credibility during the closed-door hearing as they have for several months now — pointing out that MLB’s investigators paid Bosch for his evidence and offered to drop him from a lawsuit if he cooperated with their probe. They may also point out that Bosch is the subject of federal and state criminal investigations in Florida and that he was fined $5000 by the Florida Department of Health for holding himself out as a doctor.

By claiming that he was given banned drugs when he thought he was getting legal supplements Rodriguez is tearing a page from the playbook that guided other tainted athletes. Barry Bonds told a grand jury in 2003 that he thought the creams he got from his BALCO-affiliated trainer Greg Anderson were something like flaxseed oil. Roger Clemens claimed he thought the intramuscular injections he got from his trainer Brian McNamee were shots of vitamin B-12 and lidocaine.

The alibi got Clemens into trouble when he couldn’t explain why the injections took place during furtive visits to supply closets and an upper East Side apartment and why he needed an unauthorized strength coach to give him shots instead of a team doctor.

Such claims have met minimal success in courtrooms but they sometimes work in the confidential confines of a sport’s drug program. Olympic sports have the highest standard of what is loosely termed “strict liability” where an athlete is almost always held responsible for substances found in his or her specimen regardless of intent.

But baseball’s drug policy allows players to challenge doping bans by proving a positive drug test was not due to fault or negligence and numerous players have turned to that strategy. In the Biogenesis case — which is not based on positive tests but on evidence gathered in an MLB investigation — several players accepted bans despite having explanations for their use.

Nelson Cruz of the Texas Rangers claimed to have taken substances obtained from Bosch because of a stomach ailment that caused him to lose 40 pounds yet in a statement accepting his ban Cruz said he “decided to accept this suspension and not exercise my rights under the Basic Agreement to appeal.”