The 2021 Cox Plate winner, State Of Rest, has been retired to stud, with trainer Joseph O'Brien announcing the news to the media on Tuesday night.

The four-time Group 1 winner was set to come back to Australia in the coming weeks as he attempted to defend his crown in the nation's premier weight-for-age race, setting up for a mouth-watering rematch against star four-year-old Anamoe.

O'Brien said an issue found by Racing Victoria could be the reason behind State Of Rest's last-start failure in the Group 1 Prix Jacques Le Marois, so he will be retired to stud immediately.

“Everyone here at Carriganog Racing is so disappointed that State Of Rest's racing career has come to a sudden end,” O'Brien said.

“He was without question a remarkably talented, durable and consistent performer. We asked a huge amount of him throughout his career and he delivered every time.

“He won Group/Grade 1 races on three different continents in the face of a wide variety of tracks, ground conditions and race tempos. It all came alike to him. He had the most incredible constitution and will to win.

“We'll miss him greatly, but we look forward to training his progeny in the years ahead.”

State Of Rest has subsequently been removed from Cox Plate betting markets, which has seen last year's runner-up, Anamoe, firm into outright favouritism ahead of Zaaki.

With just over 50 days until the 2022 Cox Plate, it is shaping to be an edition void of international representation.