Popular chaser Monet's Garden has been retired and "is battling away for his life", said trainer Nicky Richards.
The bold-jumping grey, who turned 13 on New Year's Day, is critically ill after suffering an infection in a foot.
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He was last seen winning the Old Roan Chase for the third time at Aintree in October, but it was reported after the race that he had a problem with a foot.
The injury became infected in the navicular bone area, which required several operations, but the wound has taken far longer than anticipated to heal.
Richards said: "The old horse is battling away for his life.
"I spoke to our vet this morning. It has been a hell of a job trying to close this infection down.
"The navicular bone became infected and it's into the flexor tendon as well and the infection is taking some closing down.
"The lady looking after him has done a fantastic job."
Richards added: "We've searched worldwide and we've been in contact with everybody looking for a way to treat it and this girl seems to have everything covered.
"She really has tried her best. He's had the best treatment available.
"Regarding his racing career though, that's over. We are just trying to save the old horse now, he's still at the vets.
"I don't know if he's over the worst yet, even. We are having a hell of a job closing this infection down.
"If we can do it, it will be absolutely fantastic."
The Roselier gelding began life in an Ayr bumper in 2003 and ran out a half-length winner.
He then won his first two races when switched to hurdles the following season before finishing second in the 2004 Mersey Novices' Hurdle at the Grand National meeting.
He returned to Aintree 12 months later to land the Liverpool Hurdle, but he excelled over fences.
Monet's Garden was triumphant on his first two starts in his novice campaign before finishing runner-up to Voy Por Ustedes in the Arkle, after which he landed a Grade Two event at Ayr.
The following season he won the Grade One Ascot Chase and finished fourth in the Ryanair before striking gold in the Melling Chase at his favourite course, Aintree.
He also beat Kauto Star in the 2007 Old Roan, but did not win again until the Peterborough Chase of 2008.
A 2009 victory in the Old Roan, and possibly a career highlight win in last year's Ascot Chase, showed age had yet to catch up with the popular chaser.
He then illustrated back at Aintree in October – his first start of the season – that all of his ability remained intact when victorious for a third time in the Old Roan.
Monet's Garden has been owned throughout his career by David Yates, who was understandably left distraught by the news.
He said: "I'm very sad for the horse because we were hoping to give him one or two more races and then look forward to a happy retirement, but it's not looking like that will be the scenario, unfortunately.
"This bone infection has really got a hold but, as he has done all his life, he's fighting.
"Whilst he's fighting, we're fighting with him.
"It's a really nasty injury but it didn't show up straight away. It was about a week after the race it was spotted.
"He's irreplaceable, I wouldn't even think of trying to replace him.
"I actually thought his best race was in the Arkle when he was only just beaten by Voy Por Ustedes trying to give him 5lb.
"Everybody said he didn't like Cheltenham but it was actually the overnight stopovers he didn't like.
"Because of that we used to take him down on the day to the likes of Ascot.
"He won the Ascot Chase twice and we were hoping he might have won it for a third time.
"He's won the Old Roan Chase three times, the Peterborough Chase, and he's also beaten Kauto Star, which not many have done.
"He beat Poquelin in the Old Roan so even though he's 13 he was as good as ever - that's because he's been looked after very well by Nicky and his daughter.
"He's been a star for us all."