James Motherway has been forced to rule Bluesea Cracker out of Saturday's rearranged Coral Welsh National at Chepstow.
Last season's Irish Grand National winner had been third-favourite with the sponsors at 9-1 following a decent run behind Midnight Chase at Cheltenham in November.
However, the nine-year-old mare knocked herself when walking in the sea near Motherway's County Cork yard last week and the injury has not settled down in time for her to take her chance.
"Unfortunately last Thursday morning she was having a little bit of exercise on the beach nearby and she just took a false step in the water and knocked into her front joint," said Motherway.
"It's not going to rectify itself in time for the weekend. I've just had a consultation with my vet who checked it again and he's not happy with it so we've had to draw a line through it unfortunately.
"If the race had been run on its correct date (December 27) she'd have been there, but there's nothing you can do about it. It's unfortunate and the owners and myself are all disappointed, but that's racing. It's nothing serious but it's enough to put us out of Saturday's race.
"She loves it soft so it looked the ideal race for her.
"I've nothing concrete in the pipeline and I'll just see how this joint settles down over the next week or two."
Lucinda Russell's grey Silver By Nature will have to carry top weight following his victory in a valuable event at Haydock last season.
Last year's winner Dream Alliance is next in the list for Philip Hobbs, but he has been pulled up in his last three races.
Tony McCoy's expected mount, ante-post favourite Synchronised, will aim to give the perennial champion jockey his first win in the race.
The Welsh National is the only one of the four 'Nationals' McCoy has yet to win.
He famously landed the Aintree version at the 15th attempt on Don't Push It, won the Scottish version on Belmont King in 1997 while Butler's Cabin won the Irish National 10 years later.
Paul Nicholls's novice Watamu Bay is another high up in the weights, while teenagers Eric's Charm, Hello Bud and Knowhere are still engaged.
Exmoor Ranger, Summery Justice and Maktu are others to note.
Noel Meade has withdrawn Pandorama, but Irish compatriot Willie Mullins could still be represented by Arbor Supreme.
Following Bluesea Cracker's withdrawal, McCoy's mount is now the 11-2 market leader.
"We are delighted that most of the principals look like taking their chance in the rearranged Coral Welsh National, the 38th running of the race under our sponsorship, and hopefully the weather will not prevent AP McCoy from attempting to complete his set of National wins on Saturday," said Coral's David Stevens.
Coral Welsh National - sponsors bet:
11-2 Synchronised, 8-1 Maktu, 12-1 Dance Island, Dream Alliance, Watamu Bay, Summery Justice, 14-1 Silver By Nature, 16-1 Exmoor Ranger, Hello Bud, Master Overseer, 20-1 Arbor Supreme, I'moncloudnine, 25-1 Giles Cross, 33-1 Bar
Donald McCain would like to get another run into Wymott before he steps up in grade to contest the totesport.com Towton Novices' Chase at Wetherby on February 5.
Trevor Hemmings's charge created a favourable impression when winning his first start over fences in a hot race at Bangor.
However, the seven-year-old, a Grade Two winner over timber, was lengthened by some bookmakers for the RSA Chase after struggling to land the odds at 1-2 on his next start at
He is a general 16-1 shot for the Cheltenham contest at present behind 7-2 market leader Time For Rupert.
"We're looking towards the Towton at Wetherby, but we might give him another run first as he's very well," said McCain.
"It's been difficult with the weather and we haven't discussed a plan, it's just a matter of getting work into him at the moment."
Sublimity made the most of a significant drop in class as he got back to winning ways with a workmanlike victory in the
McCarthy Insurance Group Hurdle at Cork.
Winner of the Champion Hurdle in 2007 but successful only once since, the Robbie Hennessy-trained 11-year-old travelled with his old dash at the rear of the four-runner field as Newmill opened up a huge early advantage.
Ridden for the first time by Andrew Lynch and massively favoured by race conditions, he had closed the gap going to the third-last but 2006 Champion Chase winner Newmill proved game in front and the pair were upsides jumping the last.
Sublimity had to fight from there but just had the extra edge in speed on the run to the line, prevailing as the 11-10 favourite.