Olympic time-trial champion Tyler Hamilton, captain of Switzerland’s Phonak cycling team, is reported to have failed two doping tests over the past month.
If a further test confirms preliminary results, Hamilton will become the first victim of new controls on performance-enhancing blood transfusions.
United States-born Hamilton apparently failed tests at last month’s Olympic Games in Athens and at the Vuelta cycling tour currently underway in Spain.
According to Phonak spokesman Georges Lüdinger, both so-called “A” tests showed a “presence of a mixed red blood cell population, indication of a homologous blood transfusion”.
A “B” test designed to confirm the preliminary results was planned for Tuesday.
Lüdinger said that Hamilton had denied undergoing a transfusion – seen as a way of boosting an athlete’s performance by increasing his or her red blood cell count.
“Tyler told us he did nothing,” he said.
The Lausanne-based International Olympic Committee (IOC) said it was waiting for more evidence.
“As with all doping procedures, while a process is underway, we can’t go into details,” commented IOC spokeswoman Giselle Davies.
IOC medical director Patrick Schamasch said he could “not confirm or deny anything” before all the test results had been received.
If found guilty of a doping violation at the Olympics, Hamilton would be stripped of the gold medal he won in the men’s time trial.
Hamilton pulled out of the Spanish Vuelta after the 12th stage last Thursday, citing stomach pains.
He rode with Tour de France winner Lance Armstrong in the US Postal Service team for six years.
Hamilton left in 2001 to become the leader of Team CSC, a Danish club that won the team competition at last year’s Tour de France.
He finished fourth in the 2003 Tour de France, but pulled out of this year’s event after two weeks because of a back injury.
Hamilton joined Switzerland’s Phonak team last year. Company chairman Andy Rihs said at the time he was delighted to have signed up one of cycling’s biggest names.
His new star opened the doors for the Phonak team to join the Tour de France and at the same time helped the company to market its hearing aid products in the US.
The 33-year-old Hamilton is the second Phonak cyclist to have tested positive this summer.
Last month Oscar Camenzind tested positive for the blood-boosting hormone EPO just before the Olympic Games.
Phonak tore up his contract immediately. Camenzind, who has since announced his retirement, was also suspended from competition for two years.
swissinfo with agencies
Tyler Hamilton was born on March 1, 1971 in Marblehead, Massachusetts.
He made his professional debut form Montgomery Belle in 1995.
He joined US Postal in 1996 before transferring in 2002 to CSC, the Danish team of Bjarne Riis.
His most notable victories came in the Tour of Denmark in 1999 and the Dauphiné of 2000.
Hamilton took part eight times in the Tour de France. His contract with Phonak was for two years.