Winx could be off to Japan next month, with the world's best turf horse nominated for the Group 1 Japan Cup at Tokyo Racecourse on November 26.

However, Racing.com's Brent Zerafa has reported that the star mare is unlikely to make the journey, tweeting a statement from trainer Chris Waller on Tuesday afternoon.

"It is highly unlikely she would travel but we've nominated as a precaution," Waller said.

Should Winx progress to a third-straight win in the Cox Plate later this month, she will be eligible for a US$2,000,000 prize money bonus in the 2400m race, which is already worth more than AUD$3.5 million to victorious connections.

 The race would be the longest distance the six-year-old has contested since her victory in the Queensland Oaks in May 2015. In fact, her last loss before the start of her incredible 21-race winning streak was the ATC Oaks over the same trip.

Winx is one of three Australian-trained gallopers nominated for the Japanese feature alongside Big Duke and Admire Deus, but the latter will not take his place after suffering an injury at track work on Tuesday morning.

Three of this weekend's Caulfield Cup contenders are in the mix with Bonneval, Jon Snow and Wicklow Brave nominated, while Aidan O'Brien's star galloper Highland Reel is among several key international entries.

All Cox Plate, Caulfield Cup and Melbourne Cup competitors will also be eligible for the enormous boost in prize money, with all runners receiving a boost of at least US$100,000 if successful in the Japan Cup.