The racing career of unbeaten two-year-old Fighting Sun is in extreme doubt after he broke down following his dominant Canonbury Stakes win.

Trainer Gai Waterhouse confirmed the colt's owners have discussed retiring the youngster, such is the serious nature of a leg injury that surfaced after the Canonbury.

"They are thinking seriously of retiring him," Waterhouse said.

Fighting Sun emerged as Waterhouse's best chance of claiming a sixth Golden Slipper triumph with his impressive three-length win in the Canonbury at Rosehill last Saturday.

It was the second victory in as many starts for the son of the ill-fated sire Northern Meteor.

But less than 24 hours later he was being treated by vets and his autumn carnival was effectively over.

Now with his racing days almost certainly numbered, Fighting Sun will stand his first season as a stallion at Eliza Park International where he will join Black Caviar's sire Bel Esprit on the Victorian farm's roster.

If he is retired without racing again, Waterhouse said the colt had an obvious selling point to Australian breeders.

"He will go to stud as the fastest, unbeaten two-year-old son of Northern Meteor," she said.

"He's a very sexy proposition."