Scorpion is set to be retired to stud after an injury ruled him out of the Melbourne Cup next Tuesday.
Trainer Aidan O'Brien's worst fears were confirmed after the triple Group One winner pulled up lame following track work on Monday.
He inspected Scorpion upon his arrival at Sandown racecourse in Australia and found the five-year-old lame in the off-hind leg.
Although Scorpion is suffering from what only appears a minor ligament problem, O'Brien said it was too risky to take any more chances with him.
"I would imagine he would probably be retired now because the plan was if everything was well after the Melbourne Cup, we were going to keep him in training next year," the Ballydoyle handler said.
"But when he has an injury like that and he's a very important horse - you couldn't take a chance with him."
O'Brien had high hopes for Scorpion after the disappointment of stablemate Yeats' seventh place last year.
"He's a little bit quicker at this stage of his life than Yeats was and he was a Group One winner - he's a very, very good horse so it's a pity for everybody," he added.
The son of Montjeu, whose big-race triumphs include the 2005 St Leger and this season's Coronation Cup, was as low as 11 to 1 to win the Melbourne Cup off top weight.
Mahler will still represent O'Brien in the "race that stops a nation", with local jockey Stephen Baster set to be in the saddle. "He looks in good shape and the staff are very happy with him," added the trainer.
"To win the Melbourne Cup would be unreal but you can't come here and expect to win it. It is so competitive and such an unbelievable race."
Scorpion's setback exacerbates a wretched few days for O'Brien, whose Breeders' Cup dreams ended in despair after George Washington was humanely destroyed after the Classic on Saturday.
Meanwhile, Aintree specialist Hedgehunter has begun steady work and is described as being in "great form" by Co Carlow handler Willie Mullins.
Owned by Trevor Hemmings, the veteran chaser enjoyed his finest hour when coasting to success in the Liverpool feature back in 2005.
Hedgehunter found only Numbersixvalverde too good the following year but could only manage ninth in the race when last seen back in April.
He reappeared over timber at Thurles last season but Mullins is yet to formulate a plan for the 11-year-old at this early stage of the current campaign.
He said: "Hedgehunter is back with us and is doing steady work. He hasn't done any fast work yet and I don't have any plan for his first run of the season at this point. But he's back and he's in great form."
Supreme Novices' Hurdle hero Ebaziyan is on course to return to action in Friday's Anglo Irish Bank Hurdle at Down Royal. In what could prove an informative renewal of the two-mile, Grade Three event, the Cheltenham Festival victor could lock horns with a host of smart recruits.
Among the potential opposition is Edward O'Grady's Catch Me, impressive Galway Hurdle winner Farmer Brown and the Dermot Weld-trained Bobs Pride.
Of Ebaziyan, who belied relative inexperience and a big starting price to win at Cheltenham, handler Willie Mullins said: "I think he'll run and he had a nice time out at grass this summer. He worked this morning and Ruby (Walsh) rode him. We were very pleased with him."
Ebaziyan must bounce back from a disappointing run in the Champion Novice Hurdle at Punchestown, but Mullins is inclined to forgive his grey that one poor showing. "He had a little setback before Punchestown and that might have just affected him, so I'm keen to give him the benefit of the doubt," he added. "We've nothing in mind further on at the moment and we'll just play it as we find it this season."
Also among the 15-strong list of entries are Noel Meade's pair Aitmatov and Orbit O'Gold, Gordon Elliott's Salford City and the promising Grangeclare Lark.
Connections of Cheltenham Festival winner Cloudy Lane have yet to decide whether their seven-year-old will make his seasonal reappearance this week. Owned by Trevor Hemmings, the promising second-season chaser holds entries in the bet365.com Handicap Chase at Wetherby on Friday and Sunday's Colin Parker Memorial Intermediate Chase at Carlisle, in which My Way De Solzen appears among the entries.
Cloudy Lane, who landed a gamble in the Fulke Walwyn Kim Muir Challenge Cup in March, enjoyed a racecourse gallop last weekend and could be aimed at the €71,000 Garswood Handicap at Haydock on November 24th. Trainer Donald McCain jr said: "I'm not sure yet whether he'll run as I have to speak to Michael Meagher, Mr Hemmings' racing manager, first.
"But the horse is well and had a gallop at Aintree on Sunday night, which went well."
