Grand National 2020: Tiger Roll 'not certain' to line-up after being given top weight for Aintree
Tiger Roll is not certain to be aimed at a record third successive Grand National win after being given top weight, says the owner's racing manager.
Eddie O'Leary said he was "disappointed" at Tiger Roll's weight, compared with other contenders.
The 2018 and 2019 winner, trained by Gordon Elliott, has been given 11st 10lb alongside stablemate Delta Work.
"He really is not certain to line up," said O'Leary.
The National takes place at Aintree on 4 April.
Last year's race saw Tiger Roll become the first back-to-back winner of the big Aintree race since the legendary Red Rum in the 1970s.
The 10-year-old would be the first horse since 'Rummy' in 1974 to win off top weight.
O'Leary told the Racing Post: "Delta Work is our Gold Cup horse and the handicapper thinks Tiger Roll is as good as him, that makes no sense to me at all.
"Tiger Roll is a brilliant, brilliant horse and he is completely invaluable to us, but we have to do our best by the horse."
Each contender is allotted a different weight based on their form as the National is a 'handicap' chase.
The next horse in the weights is Bristol De Mai (11st 8lb), trained by Nigel Twiston-Davies.
Other leading contenders include last year's Willie Mullins-trained Irish National winner Burrows Saint (10st 10lb) and Warwick's Classic Chase victor Kimberlite Candy (10st 4lb) owned by JP McManus.
Red Rum won the race three times - in 1973, 1974 and 1977 and was second in the intervening years.
Tiger Roll is owned by Gigginstown House Stud - led by airline boss Michael O'Leary and his brother Eddie.
The O'Learys have long suggested he might not run at Aintree if the handicapper is considered to have treated their horse unfairly, although many believe they will not easily turn down a chance at making racing history.
He has not run since last year's National when he won by two-and-three-quarter lengths from the mare Magic Of Light, who at 10st 12lb is 4lb better off this time comparatively with the 2019 victor.
Tiger Roll is expected to have a similar preparation this time, with Sunday's Boyne Hurdle at Navan, followed by the Cross-Country Chase next month where he would be seeking a fifth Cheltenham Festival win.
Handicapper Martin Greenwood said it was arguably the "highest quality Grand National in modern history".
He added: "The race is full of top-class individuals and boasts the winners of races such as the Grand National, Irish National, Welsh National, Cheltenham Gold Cup and much more."
BBC racing correspondent Cornelius Lysaght
I'm sure that this will he, won't he saga over Tiger Roll is going to rumble on, but if a horse wins perhaps the hardest jumps race in the world twice, it's inevitable he's going to have to 'pay' for it with less favourable weight terms.
Anyway, let's hope he runs and chases history.
Former winner One For Arthur has been given a weight that gives him a right chance; I'm sure that Walk In The Mill, fourth in 2019, will be bang there again; Potters Corner looks very fairly treated; and the 'improver' with a good weight may be Burrows Saint.