Former ASADA head Richard Ings also dismissed the possibility.
"Clenbuterol is not present in the Australian food chain. It is not present in the New Zealand food chain, it has occurred in China and Mexico but it is not an issue here," Ings told 3AW.
"So the players will need to find the right explanation where this Clenbuterol came from.
"It's a veterinary drug in Australia, it's a veterinary drug in New Zealand, it's only approved for use in racehorses.
"But as with all these performance enhancing drugs you can get it online and there is a person at the back of some gyms that will sell it to you. It is commonly abused in bodybuilding and other sporting activities."
Keeffe and Thomas have denied knowingly taking the drug and have sought independent legal advice through the players' association.