LONDON - Four-time Tour de France winner Chris Froome failed a drugs test during the Vuelta e Espana race in September, cycling's governing body UCI said on Wednesday.
The British Team Sky rider had twice the permitted level of legal asthma drug Salbutamol in his body.
The UCI has asked Froome to provide more information but has not suspended him.
Team Sky said Froome had suffered from asthma since childhood.
"During the final week of the Vuelta, Chris experienced acute asthma symptoms. On the advice of the Team Sky doctor, he used an increased dosage of Salbutamol (still within the permissible doses) in the run-up to the 7 September urine test."
The team said Froome had declared his use of the medication, adding: "The notification of the test finding does not mean that any rule has been broken."
Froome won the Vuelta general classification, with team Bahrain-Merida's Vincenzo Nibali second and Team Katusha Alpecin's Ilnur Zakarin third.