found in Contador's samples, he said, "I couldn't tell you."

If the UCI decides to pursue disciplinary action against Contador, the case will first be referred to the Spanish cycling federation for a hearing. If found guilty, Contador would be stripped of his Tour title and face a ban.

Contador has suggested he might quit the sport regardless of the outcome of the investigation.

"I understand the athlete has been barraged by media, particularly the Spanish media," McQuaid said. "He's in a pretty difficult situation. I can understand that and I have sympathy for him in that situation."