The World Anti-Doping Agency dismissed Tour de France champion Alberto Contador's claims his positive test was the result of tainted meat, saying on Wednesday they had heard the excuse before.
The Spanish cyclist was provisionally suspended by the International Cycling Union (UCI) after testing positive for a very small concentration of a banned anabolic agent during this year's Tour de France.
Contador claims the presence of clenbuterol in his system was due to contaminated meat containing minute traces of the substance.
"It's been raised before, it's been heard in a couple of cases and rejected," WADA director general David Howman told reporters during a meeting at the anti-doping agency's headquarters. "It's not unusual.
"The issue is, can you prove it? It's a pretty hard thing to prove that is where it (the banned substance) comes from.
"The tribunal will make a decision and I'm comfortable with that," he added.
WADA said it was closely monitoring the Contador case and was prepared to step in if a hearing cannot be arranged in a timely manner.
"It took a year to set the Landis hearing up the first time around," said Howman, referring to disgraced American cyclist Floyd Landis.
"If we were concerned about the results management system and that there was procrastination we can take it straight to CAS and say: 'this is wrong'.
"The issue for us is when will they have a hearing?
"At some stage somebody is going to have to say, 'here is the hearing date'."
TWO FRONTS
When a hearing is set, Contador may have to defend himself on two fronts after reports that plastic residues were found in his blood along with the steroid, suggesting the cyclist might have also undergone transfusions - which are banned under WADA's anti-doping Code.
Olivier Rabin, WADA's science director, said while there are tests capable of detecting plastic residues in blood they have yet to develop a stand-alone test for plasticizers that can link them directly to doping.
"There are residues. We're sure about this at that level, that is a scientific fact," explained Rabin. "How you connect that to doping is the question.
"Today, we cannot make a 100 per cent connection between high plastic residues to 'You are doped.'
"That is something we are working on."
Rabin conceded there were other explanations for the presence of plasticizers, which can enter a person's system through drinking out of plastic containers or eating meat that has been wrapped in plastic.
"When there are high plastic residues, we get some indications that this is very likely related to transfusions," said Rabin. "But we need to do a little more work to see whether this link is 100 percent.
"Because it's not fully validated, we can use this as an indication but don't use it as a standard of proof.
"We cannot be 100 per cent sure it was a transfusion, other explanations are possible."
