Tiger Roll will have to defy a 9lb-higher mark if he is to become the first horse since Red Rum to win back-to-back renewals of the Randox Health Grand National at Aintree.
Gordon Elliott's charge carried 10st 13lb to victory last year - but has been saddled with 11st 1lb in the initial weights for this year's renewal on April 6.
Tiger Roll only had a head to spare from the Willie Mullins-trained Pleasant Company last year and that rival is off a 7lb-higher mark, with a starting point of 10st llb.
Both Elliott and Mullins are well represented, with The Storyteller (11st 3lb) and General Principle (10st) notable possibles among 22 for Elliott, while his main Irish rival has Rathvinden (10st 10lb) and Up For Review (10st 2lb) on his 10-strong entry sheet.
While clearly unlikely to get all of his entries into the race, Elliott - who also struck in 2007 with Silver Birch - fully intends to run as many as possible in the £1million spectacular.
He said: "I'll run as many as I can. I've won it before and it would be nice to win it again.Basically I'll run whatever gets in. If I can get 10 to 15 in, I'll run them all.
"We look forward to it. Obviously it's a race we target and want to win. It will be very hard for Tiger Roll. He's got a lot more weight this year, but we'll see what happens.
"He's very good. He'll run in the Boyne Hurdle in Navan this weekend and then go to Cheltenham for the cross-country again.
"Obviously we have Dounikos and General Principle, who ran well in the trial at Punchestown. They'll be going. We'll try to get them all in because if you're not in, you can't win."
Mullins, who trained the 2005 National winner Hedgehunter, said: "I was delighted with Pleasant Company last year (second), but never thought he was going to get there. Maybe he will this year. It's been the main plan for him this year, as it has for a few others.
"Rathvinden may go for the Bobbyjo Chase at Fairyhouse or the Leinster National at Naas. Those are the two races most of mine will have to go for as there are no other suitable ones. It will probably be Naas for him.
"Up For Review ran well in the Thyestes after Paul (Townend) took him wide. I hadn't realised how well he ran - it was a fantastic trial.
"Polidam and Isleofhopendreams might not get in. Livelovelaugh ran well the other day and needs further.
"I was disappointed with Some Neck the other day, while Pairofbrowneyes still needs to qualify despite having won over two miles and seven and a half furlongs at Gowran - which would be like four miles elsewhere!
"Total Recall might run too free for a National horse. Acapella Bourgeois could be a nice horse, but has had his problems. If I could get him back he could be anything."
Nigel Twiston-Davies' multiple Grade One winner Bristol De Mai heads the weights on 11st 10lb, on a lowered rating of 168, with the Naunton handler also counting impressive Sky Bet Chase victor Go Conquer (10st 13lb) and 2017 Becher Handicap Chase winner Blaklion (10st 12lb) among his nine entries.
Twice the winning trainer of the National, through Earth Summit (1998) and Bindaree (2002), Twiston-Davies said: "I'd love Bristol De Mai to have a go. The Gold Cup is his main objective, but if he comes out of that with flying colours, then why not have a go at the National?
"Then we've got Blaklion, who was brought down at the first last year. He's now got a more manageable weight, so let's hope for him.
"Go Conquer did nothing wrong at Doncaster the other day and Ballyoptic is a lovely horse, so we've got a strong team."
Tony Martin's Anibale Fly finished fourth last year and has been given 11st 6lb this time, with Welsh Grand National winner seven-year-old Elegant Escape (11st 4lb) another leading contender for Colin Tizzard.
Owner Trevor Hemmings would become the most successful owner in the race's history if he can win a fourth renewal and his potential representatives include the Nick Alexander-trained Lake View Lad (10st 11lb) and Grand Sefton scorer Warriors Tale (10st 9lb).
The latter is trained by Paul Nicholls, who also has Black Corton (10st 11lb) and Give Me A Copper 10st 1lb.
One For Arthur (10st 10lb) won the race two years ago for Lucinda Russell, but was unable to defend his crown last year due to injury. Other entries with proven form over the Grand National fences include this season's Becher Chase winner Walk In The Mill (10st) and dual Topham winner Ultragold (10st 3lb).
Trainer Dr Richard Newland, who tasted Grand National glory in 2013 with Pineau De Re, is chasing another victory with Abolitionist (10st 1lb), and other interesting possibles include Rock The Kasbah (10st 9lb) and Mall Dini (10st 4lb).
British Horseracing Authority handicapper Martin Greenwood framed the weights for the first time this year and explained why he had adjusted Bristol De Mai's mark.
He said: "Bristol De Mai heads the weights and his rating has been compressed by 5lb as I thought it was better to have a horse at the top of the handicap whose rating was slightly out of kilter.
"If Bristol De Mai does run then I think it was the right call to make.
"I found Auvergnat (10st 8lb) of Enda Bolger's hard to weigh up. He has a lot of cross-country form and he was the hardest one I had to deal with.
"He has been running primarily in cross-country races and they are events which are having an increasing impact on the Grand National, highlighted by Tiger Roll's success last year.
"Tiger Roll is up 9lb from his mark for last year's Grand National and Pleasant Company 7lb. I have them both on the same mark for what they were rated after last year's Grand National.
"I think there are several interesting runners like Vintage Clouds and Elegant Escape, who is towards the top of the betting and he is an improving horse and was a good second to Frodon at Cheltenham last time out, so you can see why he is one of the more fancied horses.
"At the entry stage, you needed to be around the mid-70s to get you into the race. I think anything based in the top 80 has a chance of getting in.
"Four of the last five years, horses approaching that number have got in so some connections shouldn't give up because they are rated towards the bottom."