Late climber Chris Froome is facing the toughest of challenges | Sean Ingle

Some sports stars appear destined for glory even at an early age. Chris Froome’s true ability on a bike, however, started to uncoil and manifest itself only after his mid-20s. Since then his achievements have been staggering. Four Tour de France yellow jerseys. The first man to complete the Tour-Vuelta e España double since 1978. And that rare ability to hang with the best time-triallers and nimblest mountain goats.

What makes Froome’s success even more extraordinary is that he grew up in Kenya, an athletics powerhouse but a cycling backwater, and only got into the sport, aged 12, when he asked a talented local rider David Kinjah to teach him to mountain bike. Soon the pair were regularly riding 30 miles up into the mountains above Nairobi where they would sometimes camp in a meadow. On one occasion a cow ate half their tent.

Two years later, Froome was sent to St John’s in Johannesburg, one of the most exclusive boarding schools in South Africa and more noted for its rugby players than its cyclists. It was only in 2004, when he was 19, that he watched the Tour de France for the first time. He was soon captivated by the duel between Lance Armstrong and Ivan Basso. “I was cheering for Ivan at the time,” he said. “He was the underdog. I wanted him to win.”

Froome has followed a similar road for most of his sporting life. At 21, he made it to Europe where most major road races are staged. Again his methods to get there were far from orthodox. Without anyone realising, he used the Hotmail account of the chairman of the Kenyan cycling association to email the sports governing body, the UCI, to say: “We’re going to send a cyclist to the U23 worlds.”

He turned up and after 150m of the individual time trial he rode into a race commissaire before recovering to finish a respectable 36th.

Froome turned pro the following year and showed enough promise – 84th in his first Tour de France in 2008 and 35th in the Giro d’Italia the following year – to be signed by Team Sky in 2010. Yet, at 24 years old, no one regarded him as a future general classification contender.

It was also at that stage that he decided to race for Britain. Some people, including David Millar, believe Froome chose to do so to help advance his career and “deep down he feels more African than British”. However in a recent interview with the Times, Froome insisted it was more complicated than that. “When I represented Kenya, when I was younger, that was when I felt I was cheating the system, or doing something not quite kosher,” he said. “I was representing a country and maybe taking a place of someone, shall we say, more bona fide Kenyan. As soon as I made the switch [to riding for Britain] I felt I was doing things properly, the way they should have been from the start.”

Many riders kick on after joining Team Sky. But Froome’s performances in 2010 were so up and down that it came as a relief when he was diagnosed with the tropical bug bilharzia, which he caught when he was fishing with his brother in Kenya. “It feeds on red blood cells so your immune system is always weaker and your recovery is not as fast,” he explained in 2013. “I would get chest infections and colds that lasted for weeks until I stopped training completely. In a way it was a relief when I found out.”

Yet this diagnosis did not immediately bring a change in his fortunes. Froome looked set to be dropped by Team Sky until he produced a remarkable ride in the 2011 Vuelta a España to finish second ahead of his team-mate Bradley Wiggins.

Ten months later he was a not particularly loyal wingman to Wiggins, who became the first British cyclist to win the Tour de France, and the uneasy relationship between the pair spilled out to the pair’s partners arguing on Twitter. But a second-place finish showed he was a completely different rider from only 12 months earlier.

And in 2013, with Wiggins out of the way, Froome was able to canter to his first Tour de France yellow jersey with plenty in hand. It is a thirst he has enjoyed satisfying, with further victories coming in 2015, 2016 and 2017.

Along the way Froome has faced the same question that almost every leading cyclist has to endure – are you clean? Before the 2013 Tour he described as “really sad” a suggestion in ‘Not Normal?’ – by the French journalist and former Festina trainer Antoine Vayer – that there may be suspicions surrounding him.

Vayer analysed the watts generated by 21 riders on iconic mountain stages and concluded that climbs by Marco Pantani and Lance Armstrong had been “mutant”, or highly suspicious, while Froome’s effort was merely “miraculous”, indicating possible suspicions.

Froome’s response was measured, if exasperated. “There is still a lot of scepticism out there and a lot of fans have been let down. I sympathise with that. But I know that my results aren’t going to be stripped in five, six, seven years’ time.”

However, an adverse analytical finding in this September’s Vuelta means he could well be stripped of his latest and perhaps greatest victory. He knows that he needs to provide a sufficient explanation for the abnormal finding, or challenge the result, to avoid a potential sanction from the sport’s governing body, the UCI. Team Sky say salbutamol levels can vary depending on dehydration and other factors. In a statement they said: “There are complex medical and physiological issues which affect the metabolism and excretion of salbutamol. We’re committed to establishing the facts and understanding exactly what happened on this occasion.”

Froome has got used to defeating tough challenges during his career. This, however, could be his hardest yet.