Orfevre's chances of making racing history on Sunday by giving Japan its first win in Europe's most prestigious race, the Prix de l'Arc de Triomphe, and fulfilling a nation's dream have grown immeasurably.

Japan's 2011 horse of the year Orfevre became clear favourite for Sunday's showpiece after two of his main rivals had to be withdrawn.

Last year's brilliant winner German filly Danedream and top class English colt Nathaniel followed in the wake of the heavily fancied English mare Snow Fairy, who finished third last year and had warmed up for the Arc with a brilliant win in the Irish Champion Stakes last month.

However, a leg injury after gallops last Friday put an end to her challenge and boosted trainer Yasutoshi Ikee's hopes of Orfevre succeeding where 12 others over a spread of 32 years have failed.

Tuesday, though, thrust the four-year-old colt into perhaps the unwanted territory of undisputed favourite as previous co-favourite Danedream had to be withdrawn through no fault of her own or her connections.

The villain in the piece was an unnamed German horse stabled at the Cologne racetrack who was diagnosed with an infectious equine blood disease forcing the authorities to put all the horses there into an enforced three-month quarantine.

"There is no choice but to withdraw her as while if the race had been in a fortnight we might have been able to arrange something but it is impossible now with only a few days to go," said part-owner Teruya Yoshida's racing manager Patrick Barbe.

A few hours later, Nathaniel, seen as the big danger after victory in the Eclipse Stakes earlier this season and a second to Danedream and Snow Fairy in the King George VI and Queen Elizabeth Stakes and Irish Champion Stakes respectively, was discovered to have a temperature and as a result ruled out.

"He had a temperature this morning, they took some blood tests and his blood wasn't right," said James Wigan, racing manager for owner Lady Rothschild.

"Considering how close we are to the race, we cannot consider running him."

That leaves 16 rivals for Orfevre, though, others may enter the fray on Thursday for a late entry fee of 100,000 euros ($A125,431).

One of those still in the race and who, on form, would be a major danger to Orfevre is Irish star Camelot, winner of the English 2000 Guineas and the Epsom and Irish Derbys.

Camelot's trainer Aidan O'Brien had been non committal about running him in the Arc as aside from his hard season he cannot be ridden by his normal jockey Joseph O'Brien as the trainer's son cannot make the weight.

However, O'Brien, who has just one win in the race in 2007 with Dylan Thomas, was more upbeat about his running on Tuesday.

"Obviously we're looking at it (the Arc) very strongly with the two big horses, Camelot and St Nicholas Abbey," he told RTE Radio.

"Both of them are doing a little bit in the morning (Wednesday) and if they come through that well, I think everybody will sit down and have a chat about it tomorrow afternoon and we'll see what we're going to do."