Chris Froome and Team Sky are facing a crisis that threatens their futures in the sport after the British rider recorded an adverse test for an asthma drug at La Vuelta.

A urine sample Froome gave during the Spanish race was found to contain twice the permitted concentration of salbutamol, a result that could cost him his memorable Vuelta win and see him miss May's Giro d'Italia and the Tour de France in July.

A ban for Froome, even one reduced for mitigating factors, would also place his team in an uncomfortable position because of a zero-tolerance approach to doping that has led to the release of several members of staff.

One of those was Froome's former coach Bobby Julich, who in 2012 admitted to doping as a rider on Lance Armstrong's team.

Froome, thought to be cycling's best-paid rider, extended his contract with Team Sky until the end of 2020 shortly before this year's Tour, which he won for a fourth time.

Although he is not suspended, the 32-year-old's chances of winning a record-equalling fifth Tour now seem to hinge on how he explains that adverse finding to the International Cycling Union (UCI).

Recorded after the 18th stage on September 7, the concentration of salbutamol in his sample was 2,000 nanograms per millilitre (ng/mL), double the World Anti-Doping Agency's limit of 1,000 ng/mL.

A beta-2 agonist, salbutamol is banned when administered intravenously or in pill form but asthma sufferers can take up 1,600 micrograms over 24 hours via an inhaler, without exceeding 800 micrograms (mcg) every 12 hours. A typical dosage, or puff, is 100 mcg.

In a Team Sky statement, Froome said: "My asthma got worse at the Vuelta so I followed the team doctor's advice to increase my salbutamol dosage. As always, I took the greatest care to ensure I did not use more than the permissible dose."

In a message posted on his Twitter account on Wednesday, Froome added: "I am confident we will get to the bottom of this."

He was among the favourites for Sunday's BBC Sports Personality of the Year award after becoming the first British winner of La Vuelta and completing only the third Tour-Vuelta double in history. The broadcaster declined to comment on the Vuelta issue but confirmed he remained on its shortlist.

That will mean nothing, though, if he cannot convince the UCI there is a good reason for the spike in his salbutamol concentration, with the debate likely to focus on when he took his last puff, how dehydrated he was and if anything else he was eating or taking may have had an impact.

Alessandro Petacchi was handed a one-year ban and stripped of five stage wins at the 2007 Giro after returning a salbutamol concentration of 1,320 ng/mL and fellow Italian Diego Ulissi was given a nine-month ban in 2015 after a sample from the previous year's Giro showed a similar level to Froome's.

Ulissi's attempts to explain that included trying to replicate the conditions of the day he was tested in a lab - something the UCI will insist of Froome, too.

The stakes could also not be higher for Team Sky, particularly after the long-running saga of the mystery package delivered to former star rider Sir Bradley Wiggins at a race in 2011.

UK Anti-Doping, which said it is willing to liaise with the UCI on the Froome case, has only recently announced it could neither prove nor disprove there was any wrongdoing in the Wiggins episode.

Team Sky boss Sir Dave Brailsford said: "We're committed to establishing the facts and understanding exactly what happened."