"At the 2006 Tour de France, traces of this product were found in his urine," the UCI said in a statement. "However the results of tests during the race cannot be considered as a positive anti-doping control."
But the UCI said the Spaniard had shown "serious negligence" when he delayed providing evidence of a medical exemption to the French Anti-Doping Agency (AFLD) requested in September last year.
"Although he had medical justification requested from September 2006 by the AFLD proving that he indeed suffered from asthma brought on by physical exertion, Oscar Pereiro delayed providing it to this organisation," it said.
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"This is considered as a failure to respect established administrative procedures. This serious negligence by the Spanish rider is regrettable and harms the image of cycling as a whole, although he is not guilty of any infringement."
Last week the French daily Le Monde reported that Pereiro had twice tested positive for salbutamol during the Tour. Pereiro told Radio Marca last Thursday he had had an official medical exemption since March 2005.
The UCI said it asked the AFLD to refrain from publicly implying that a rider was guilty of a doping offence when he had committed an administrative fault only.
"Such an attitude does not help to support the cycling community, which is fighting more than ever against the phenomenon of doping."
Tour de France winner Floyd Landis tested positive for the banned male sex hormone testosterone during last year's race.
He faces a two-year ban form the sport and may be stripped of his title if his appeal before a U.S. panel of judges fails this year.
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