First competing in selected rounds of the World Rally Championship in 1999, Loeb soon found his form and won a frankly ridiculous nine successive titles for Citroen between 2004 and 2012.
With his stock at its highest, Loeb tested F1 machinery on several occasions, first with Renault in 2007 and then with Red Bull in 2008 (main photo), and discussions about switching to F1 full-time gained traction the following year, when the Frenchman declared his interest in driving for Toro Rosso in the season-ending Abu Dhabi Grand Prix ahead of a full season in 2010.
Alas for Loeb, his plans were dashed when he was refused an FIA Super Licence to race in Abu Dhabi on account of not having done enough junior circuit racing, and motorsport fans the world over were denied the chance of seeing how one of rallying's all-time greats would have fared in F1.
Another crossover that might have been, it seemed during the mid-2000s that multiple MotoGP champion Rossi was being constantly linked with a Ferrari F1 seat, and he tested for the Prancing Horse on several occasions.
The first of these came at Valencia in 2006, when Rossi was soon lapping within half a second of no less than Michael Schumacher, who was said to be incredulous at the Italian's swift turn of speed.
So impressed were Ferrari that they offered Rossi a contract – but crucially insisted that he start first as a test driver and then move to a satellite team, rather than jumping straight into a Ferrari.
Perhaps mindful of being unable to emulate the success he had enjoyed on two wheels, Rossi rejected the offer and elected to stay in MotoGP, where he raced up until the 2021 season – at the ripe old age of 42.
In addition to his dalliance with Ferrari, Rossi also notably undertook a promotional ride swap with Lewis Hamilton in 2019 that saw him take the wheel of the Briton's 2017 title-winning Mercedes-AMG W08.
Seeking a career in motorsport outside his native New Zealand, Dixon moved to America in 1999 before graduating to the IndyCar series in 2003.
Six championship titles and an Indy 500 win suggests the Kiwi made the right call to head stateside, but Dixon's prowess also caught the eye of the Williams F1 team, who invited him to test the FW26 on two occasions in 2004.
Dixon was immediately on the pace, setting a best time 0.3s slower than regular driver Ralf Schumacher at Paul Ricard, but a subsequent outing at Barcelona was disrupted by bad weather and mechanical issues.
Ultimately, Dixon stayed in IndyCar for 2005 where he remains to this day, but has shown his versatility by also becoming a three-time winner of the Daytona 24 Hours, as well as competing at blue-riband sports car races at Le Mans and Bathurst.
Along with fellow Briton Dan Wheldon, Franchitti was another driver who, either by luck or judgment, ended up having a distinguished career racing in Indycar rather than F1.
But the Scot might easily have followed in the footsteps of compatriot David Coulthard by racing for McLaren. Franchitti first tested for the Woking-based squad in late 1995 and was offered a testing contract for 1997.
However, with Coulthard and Mika Hakkinen a well-established driver pairing, Franchitti figured there would be no room at the inn, and instead set about carving an excellent niche for himself stateside.
After winning regular races in Indycar, Franchitti was invited to test a Jaguar F1 car in 2000, but the Scot was not fully fit after a heavy crash earlier in the year, and with the R1 being a tricky beast to tame, the test ended in disappointment.
Undaunted, Franchitti would go on to win three Indy 500s and four Indycar titles, but one can't help wonder what he might have achieved in the F1 title-winning McLarens of 1998 and 1999.
No compendium of best drivers never to race in F1 would be complete without including Tom Kristensen.
The Dane is best known for his remarkable record in the fearsome 24 Hours of Le Mans, which he won a record nine times, including on his debut at La Sarthe in 1997, where he was a last-minute addition to the Joest Porsche squad.
But before committing to sports and touring cars, Kristensen was a race winner in open-wheeled motorsport, including Formula 3000 and Formula Nippon.
The Dane also tested for several F1 teams, including Minardi, Tyrrell and Williams, and was linked with full-time moves to Jordan, Prost and Jaguar, though ultimately nothing ever materialised.
However, given the lack of success those teams enjoyed in early 2000s F1, perhaps it was for the best that Kristensen stuck to sports cars, with his undoubted talent firmly cementing his legacy at Le Mans.
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