British road cycling champion Chris Froome has been requested by the world governing body UCI to provide more details following a failed drug test following the Vuelta a Espana earlier this year.
Froome, who races for Team Sky, had double the allowed level of legal asthma drug Salbutomol in his body, the UCI says.
He said he increased the dosage but that he was within the legal limits.
Froome, 32, said his team doctor advised him to up his usage of his inhaler after his asthma symptoms got worse during the Spanish race.
His urine test, taken on September 7, showed levels of the drug, Salbutamol, which is commonly taken for asthma, were at 2000 nanograms for millilitre (ng/ml).
That compares to the World Anti-Doping Agency's threshold of 1000 ng/ml.
Froome won the Tour de France four times (2017, 2016, 2015, 2013).