British cyclist Simon Yates tested positive for a banned substance during the Paris-Nice race on March 12 in a result his team has blamed on administrative error.
Former world track champion Yates is one of Britain's brightest prospects along with his twin brother Adam, and a strong contender to make the Olympic road race team in Rio.
Orica GreenEdge released a statement on Friday saying it was notified last week that the 23-year-old tested positive for Terbutaline, in the form of an asthma inhaler which was part of documented ongoing treatment, and which the team doctor noted on the doping control forms.
But the team said the doctor erred by not formally applying for a therapeutic use exemption for the substance, and that is why the positive result was flagged by anti-doping authorities.
"This is solely based on a human error that the doctor in question has taken full responsibility for," GreenEdge said in the statement. "There has been no wrong-doing on Simon Yates' part.
"The team takes full responsibility for this mistake and wishes to underline their support for Simon during this process."
The GreenEdge statement was released in the wake of a brief British Cycling confirmation that a rider had tested positive during a race. British Cycling did not identify the rider, or the race, and said the International Cycling Union was handling the case.
GreenEdge said it was concerned by a leak of information, and would make no further comment until a full evaluation of the case "and evidence that the team and Simon Yates are now submitting to the UCI in order to clarify everything".
The sport's embattled national governing body has also denied claims made by a British newspaper that high-performance equipment provided by UK Sport has been sold on for profit.
Yates, who won gold in the points race at the 2013 Track World Championships in Minsk, made his Tour de France debut in 2014 and raced again in 2015, after opting to sign for Australian squad Orica-GreenEdge ahead of Team Sky.
Associated Press and Press Association Sport contributed to this report