International Cycling Union boss Hein Verbruggen says no action will be taken against Lance Armstrong in the wake of recent doping allegations.
French newspaper L'Equipe claimed signs of EPO were detected in samples of Armstrong's urine given in 1999.
Armstrong, who retired after winning his seventh Tour de France in July, has angrily denied the allegations.
And Verbruggen told Le Figaro: "It's not wise to condemn someone who hasn't tested positive in a legal sense."
"I'm pleased the UCI is investigating this entire matter thoroughly because any professional investigation will reveal that the allegations made by a French sports tabloid have no basis because I never used any performance-enhancing drugs," Armstrong said in a statement.
"Based on the translation I read of the press release, I'm pleased that the UCI seems to be asking many of the right questions."
L'Equipe alleged that six of the 12 positive tests from the 1999 Tour de France belonged to Armstrong.
Verbruggen said: "The normal sanction - if you can prove that someone has tested positive - is a two-year ban, but what we have here cannot be used as proof."
A UCI spokesman singled out World Anti-Doping Agency president Dick Pound for making "public statements about the likely guilt of an athlete on the basis of a newspaper article and without all the facts being known."
When the allegations were first made, Pound had said: "It's a pretty serious story if it is true."
In 2004, Armstrong wrote an open letter to European newspapers saying Pound should not be in charge of Wada.
The UCI also criticized the article in L'Equipe as "targeting a particular athlete."
The editor of L'Equipe, Claude Droussent, denied his newspaper targeted Armstrong because of his nationality and said it would have treated a French rider in the same way.
The tests in question were carried out retrospectively in 2004 at the French national anti-doping laboratory at Chatenay-Malabry, just outside Paris, to help testers improve their EPO detection methods.
"We're going to be looking further into this affair," added Verbruggen.
"It's another heavy blow to cycling so we have to take it all the way. And I also want to know who exactly it was who gave out this information."
Verbruggen said the UCI had the names of the other six riders that allegedly tested positive.
"We're waiting for answers to our questions from the laboratory to see what can and should be done," he said.
The 33-year-old Armstrong, who is set to marry rock star Sheryl Crow, is considering coming out of retirement in response to the allegations.