Bookmakers are estimating a £50million pay-out should Shutthefrontdoor land the Crabbie's Grand National and give Tony McCoy a dream swansong from the saddle at Aintree.

But McCoy reckons his wife would only back Shutthefrontdoor if he did not tell her to.

"Chanelle thinks I'm the worst tipster in the world," he said. "If she was thinking of having a bet on the Grand National, she'd back me as long as I didn't tell her to - if I told her to bet on me, she'd probably back something else!"

Oh his chances of winning, which would lead him to retire on the spot, McCoy said: "That would be a bit of a fairytale and I'm not even sure I'm silly enough to dream that could happen. There would be a bit of sadness too, knowing that it would be the last time I'd ever be on a horse."

Betfair's Barry Orr said: "With over 4,000 winners AP has built a house that will never fall and Saturday's race will be the last piece of an amazing puzzle when he shuts the front door on an outstanding career.

"But an AP victory will not be welcome by bookies and even though he has been socking it to us for over 20 years, a win on Saturday would be the biggest single loss incurred by the betting industry on one of his winners."

Hills spokesman Jon Ivan-Duke said: "It's the calm before the storm, we've obviously seen interest in McCoy's horse but there is an ominous feeling. The betting clouds are building but it's the biggest race of the year, we won't be running for cover and we'll try and ride out the inevitable onslaught."

Paddy Power pointed to a small chance that something could actually challenge Shutthefrontdoor for favouritism.

He said: "While it's still highly likely that the AP factor will send Shutthefrontdoor off a clear favourite, it's still not impossible that a plunge on another horse such as Rocky Creek could usurp him come the off on Saturday."

Warren Greatrex could not be happier with both Dolatulo and Tranquil Sea as he eagerly awaits the weekend.

The Upper Lambourn trainer reports his two runners to be at the top of their game ahead of the world famous steeplechase.

"Dolatulo and Tranquil Sea both schooled over fences on Tuesday and both look a million dollars," he said.

"All their work is now done and we are just counting down until Saturday now."

Charlie Longsdon may be saddling a big outsider in Ely Brown, but that is down to the 10-year-old having been out of action for some time and not to his ability.

Longsdon has not booked a jockey yet and will wait until after final declaration time on Thursday.

"We will see what happens at declaration time and then we'll make a decision," said the Chipping Norton trainer.

Longsdon reports Ely Brown to be ready to show his true colours after recovering from the problems that have kept him off the track for most of the season.

"The horse is in good form. He had an injury this time last year which kept him out then he had a wind op, so he hasn't had a chance to shine yet this season," he said.

"He's a fresh horse, he's done nothing this season.

"He's won a few big handicaps over hurdles and was sixth at the Cheltenham Festival and he's won a Grade Two over fences.

"He's not a real 100-1 shot if you look at that form. He's only that price because he hasn't run this season except when he was pulled up, but he had a wind problem."

Aidan Coleman believes his mount, The Druids Nephew, was one of the best rides he could possibly have picked up.

With his usual partner Barry Geraghty injured, trainer Neil Mulholland was on the lookout for a suitable jockey and went for Coleman.

"It is definitely one of the best rides to pick up. Phil Smith, the chief handicapper, says he is the best handicapped horse in the race," Coleman told the Daily Mail.

"The race should suit this horse. He seems quite hardy. He handled the hustle and bustle of the Cheltenham Festival and came out a very nice winner."

Gordon Elliott, who landed the National with Silver Birch in 2007, is hoping the ground continues to improve to boost the chance of Cause Of Causes.

The seven-year-old, who is owner JP McManus' second string behind Shutthefrontdoor, showed his well-being when winning the four-mile National Hunt Chase at Cheltenham last month.

"He's in good form. The more the ground dries out, the better he'll be," the County Meath trainer said.

"He jumped four National fences up on the Curragh last week so we're very happy with him."