The Last Word: Arc brings Dettori and the Sheikh to a strange junction

Dettori is expected to count his millions as fair exchange for his self-respect

Anyone who has careered round L'Etoile at the mercy of a Parisian taxi-driver knows exactly what kind of white-knuckle ride awaits the jockeys who tomorrow contest the richest prize on the European Turf. For the Brownian convulsion of horseless carriages in that vortex will be replicated in the Prix de l'Arc de Triomphe by 18 thoroughbreds, jostling round the bends and staccato straights of Longchamp, just a couple of miles from the eponymous monument to Austerlitz. And, in the process, the island that once gave France an emperor may again find itself agent of seismic change.

Unlike Napoleon, Mickael Barzalona was not actually born in Corsica. But his grandfather trained there, and holidays at the stable introduced Barzalona to a profession that happens to trace one of its modern masters to the adjacent island. For his emergence as the most exciting new talent since Frankie Dettori, over 20 years ago, has also thrust Barzalona into direct competition with a man who cherishes his Sardinian ancestry. Now, in the Arc, Dettori has finally been provoked into a spectacular stand – in defence of both his professional dominion and personal dignity.

The Italian partners Camelot, the Derby winner, whose regular jockey cannot make the allotted weight. Nobody could surpass Dettori's sense of direction in the blind alleys of a race he has won three times, from 24 consecutive attempts, and his availability should in principle have qualified him as automatic choice to fill the vacancy. But Camelot is trained by Aidan O'Brien for John Magnier and his partners at Coolmore Stud, whose rivalry with his employer, Sheikh Mohammed, has long shaped Dettori's career.

In 2005, Dettori won O'Brien the St Leger on Scorpion – for which perceived offence to his boss he soon expressed public contrition. He has not ridden for the Ballydoyle trainer since. In the meantime, however, much has changed. And the Sheikh, who cherishes a reputation as both loyal and far-sighted, must surely acknowledge as much.

In March, the Sheikh hired Barzalona to join his Godolphin stable. Barzalona had been working for André Fabre, the record-breaking French trainer who nowadays also nurtures young equine talent for Godolphin. Last year the pair combined to win the Derby – for Coolmore, funnily enough – with Pour Moi. Barzalona rode with unforgettable brio, with tactics that abandoned every Epsom convention. He was still only 19, and the Sheikh was captivated.

Dettori had been Godolphin's No 1 jockey since the stable's inception, two decades ago. From the moment he arrived, however, Barzalona was indulged with parity. Not only would he retain the mount on any winners he rode. In May, Godolphin had one last chance to find a Derby colt. Mandaean, imported from Fabre's stable, was entered for the final big trial and the Sheikh decided Barzalona should ride. As it turned out, Mandaean ran deplorably. Dettori doubtless knew he was not missing out on anything special. To outsiders, however, it had looked a calculated affront.

In effect, Dettori is being expected to count the millions he has earned in the Sheikh's service as fair exchange for his pride, if not his self-respect. One way or another, Dettori has weighed up the opportunity to ride Camelot and reached a different conclusion. And if the Sheikh wants to reinforce his image as a generous patron, immune to sycophancy and vain trifling, he must treat this ostensible apostasy with due latitude.

For one thing, the mutual froideur with Coolmore, which intensified into something akin to downright feud around the time of Scorpion, seems to have thawed somewhat over the past couple of years. More significantly, however, the Sheikh should not presume that paying him a fat salary all these years necessarily absolves him of all debt to Dettori. For the fact is that the Mandaean debacle was hardly untypical of Godolphin's failure to build on its spectacular early success.

Dettori's pomp has been consumed by obligations to an empire that has not matched investment with dividends. Then, last month, he watched Barzalona end Camelot's unbeaten record with a superlative ride on Encke in the St Leger. Encke is one of just three elite winners in Europe this season, for the two main Godolphin trainers; Camelot's defeat, in contrast, confined O'Brien to four wins and a close second in the five British Classics.

Tomorrow Barzalona rides Masterstroke for Fabre, in Godolphin silks. It would be bordering on spiteful for the Sheikh to require Dettori – who had expected to ride the top-class Snow Fairy with impunity, until her withdrawal through injury – to watch the race on the changing-room monitor, rather than from Camelot's saddle.

If the Sheikh feels truly traduced, however, then perhaps this will prove as bewildering a junction in their relationship as L'Etoile itself. The Ballydoyle stable jockey is O'Brien's son, Joseph, whose longevity in the role is menaced by physical maturity. The teenager has already spoken of an eventual switch to jumping, with its higher weight scale. At 41, Dettori remains in his prime, more seasoned than Barzalona and O'Brien Jr put together. However unmistakably Barzalona's panache evokes his own rise, it is premature to expect Dettori merely to light the way for his heir.

If only for tomorrow, at any rate, he is merely obeying the axiom. If you can't beat them, join them.