The rule that prevents Dwain Chambers from going to the Beijing Games will not stand up in court, says the ex-boss of the World Anti-Doping Agency (Wada).
Dick Pound believes the British Olympic Association (BOA) by-law that bans drugs cheats from competing for Team GB does not comply with Wada legislation.
Chambers, who failed a drugs test in 2003, is considering a legal challenge.
"As a matter of law, I think the BOA would be on pretty shaky ground," the 65-year-old Pound told BBC Sport.
"If the BOA sought to deny me a place in the 2008 Olympic team on the basis solely of my earlier drugs offence, I would say that they don't have the power to do that.
"If you serve the penalty that was deemed appropriate - for whatever the offence was - you are entitled to be reintegrated into society"
"I've always felt it was fairly clear what the outcome (of a challenge) would be."
By-law 25 has been on the BOA's statute book since 1992, when the then chairman Sir Arthur Gold decided Britain must take the moral high ground in the fight against doping.
The BOA is now the only national Olympic committee to maintain this hard-line stance but says it will "vigorously" defend any attempt to remove the anti-doping by-law.
There have been 26 successful appeals against the lifetime ban over the last 16 years - the last being 400m world champion Christine Ohuruogu's - but nobody has challenged the actual legality of the rule in the courts.
Pound's comments will greatly concern Britain's Olympic chiefs, particularly as the Canadian is a leading candidate to become the next president of the Court of Arbitration for Sport (CAS), world sport's top appeals body.
Chambers was banned from athletics for his part in a doping scandal that continues to generate headlines on both sides of the Atlantic.
The Bay Area Laboratory Co-Operative, or Balco, started life as a sports supplement business but achieved notoriety for its more profitable sideline in providing performance-enhancing drugs to some of the biggest names in sport.
It was for using one of these drugs, the previously undetectable steroid tetrahydrogestrinone (THG), that Chambers was banned. The former world junior 100m record-holder was caught when a rival coach supplied the authorities with a syringe that enabled them to develop a test for THG.
Chambers, who returned from his two-year ban in 2005, is running for Britain at the World Indoor Championships in Valencia on Friday but remains banned from ever wearing the British vest again at an Olympics.
In fact, British athletics bosses did not even want Chambers in their team for Valencia but found their hands forced when his victory in the trials - which they had failed to stop him from entering - guaranteed him a spot.
606: DEBATE
And British officials are not the only ones to be upset by his presence in Valencia - Spanish Athletics Federation president Jose Maria Odriozola has told local media that Chambers will be an unwelcome guest.
"I'm not happy that Chambers is competing but we can't do anything about it because his country has included him in their team," Odriozola said.
"We have received warnings that the British fans are going to express their opposition to him being allowed to run.
"They could cause a very serious incident and prevent the race taking place because their shouting could stop the athletes hearing the gun."
This is the 29-year-old sprinter's second attempt at a comeback. His first try was initially less controversial - he was selected to represent Britain twice with little outcry - but ended in bitterness when he walked out of the sport to pursue a career in American football.
But since then the climate in world athletics has changed considerably, with some believing the sport will die if a serious stand against doping is not taken.
Pound, a practising lawyer and former vice-president of the International Olympic Committee, sympathises with this view but is concerned that any moral stand must have a firm legal basis.
"The BOA is a signatory to Wada's code - those are the rules that govern doping infractions - and the sanction for a first offence is a two-year suspension," said Pound.
"Chambers has served his ban and I think, depending on your view of criminal justice, if you serve the penalty that was deemed appropriate - for whatever the offence was - you are entitled to be reintegrated into society.
"The additional penalty of never representing Britain again can be seen as a sanction that is over and above what's in the code."
Chambers has no chance of persuading the BOA to rescind its ban - his offence does not meet any of the by-law's stated grounds for clemency - and an appeal to the CAS is also unlikely as his case would not be heard until after this summer's Olympics.
This means Chambers' only realistic route is to take the more expensive but far speedier option of going to the High Court. Much depends on his performance on the track in Valencia, but confirmation of his legal challenge is expected in the coming weeks.
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