Order Of Australia has suffered a career-ending injury and will not be able to defend his crown in the Breeders' Cup Mile next month.

Last year, the four-year-old earned a shock win in the Mile at Keeneland, beating Circus Maximus by a neck with Pierre-Charles Boudot on board.

He struggled to build on that victory this year and picked up just one win in six outings, coming home first at the Romanised Minstrel Stakes at the Curragh in July.

Aidan O'Brien's charge came home at the back of a 12-strong field when last seen in the Keeneland Turf Mile earlier this month — and that is set to be his final career outing.

Order Of Australia has sustained a small fracture that required an operation on Wednesday and O'Brien confirmed he will now go to stud.

He said: "He ran some very good races this year. At Keeneland, he was a bit slowly away and it didn't work for him but he's had a bit of a setback.

"He won't get to race again. He had a small fracture and had a pin put in it this morning.

"The operation and everything went well. He will go off to stud now."

The Ballydoyle trainer will still be represented in the November 6 contest at Del Mar by 1000 Guineas winner Mother Earth.

O'Brien also admitted he could tinker with his selections in other races as he considers switching Love from the Breeders' Cup Turf to the Filly & Mare Turf.

That move would allow first reserve Japan to get in the races, while he also has Broome, Bolshoi Ballet and Mogul as reserves for the Turf.

O'Brien added: "It is very possible that could happen. I think the American handicap system is a little bit different to ours.

"It wasn't on ratings horses were getting in. We have four Group One winners who are all reserves, so it is possible we might have to take Love out of it and run her in the Filly & Mare to give the other horses a chance to get into the Turf.

"The horses are due to fly on Saturday. We'll have an idea by then what chance they have of getting in or not."

Meanwhile, Glounthaune, who won at Leopardstown when last seen, holds entry to the Breeders' Cup Juvenile Turf after recovering from a slight setback that prevented him from running in France last weekend.

O'Brien said: "He steps up to a mile for the first time but we always thought that was within his compass of distances."