The Storyteller was the only withdrawal as the final field of 40 horses – headed by Cloth Cap – was named for the Grand National on Saturday.
It means Blaklion is the last horse to be guaranteed a run in the big race at Aintree.
Some Neck and Welsh Grand National winner Secret Reprieve are the top reserves.
Patrick Mullins will ride leading contender Burrows Saint for his trainer father Willie Mullins.
Stable jockey Paul Townend will miss the ride after suffering a foot injury.
A reserve can make the line-up if any contenders are pulled out before 13:00 BST on Friday.
Last year’s Grand National was called off because of the Covid-19 pandemic, while this year’s contest will be held without spectators.
Police are stepping up patrols around the meeting, with residents close to the Merseyside track warned not to gather in groups larger than six in their gardens during the races.
Cloth Cap, trained by Jonjo O’Neill, is the 4-1 favourite to give owner Trevor Hemmings a record fourth win in his green, yellow and white colours.
Two-time Grand National winner Tiger Roll will return to the scene of his biggest triumphs on Thursday – but in a different race at Aintree.
The 11-year-old runs in the Betway Bowl, where rivals will include Clan Des Obeaux and Native River.
It is the feature race on day one of the fixture, which culminates with Saturday’s National.
Tiger Roll was withdrawn last month from the National, which he won in 2018 and 2019.
Owners Michael and Eddie O’Leary said they were unhappy with the weight the horse had been allocated.
Tiger Roll became the first horse since Red Rum in the 1970s to win consecutive runnings of the Grand National when triumphing in 2019.
Currently trained by Denise Foster while Gordon Elliott serves a suspension, he recorded a fifth Cheltenham Festival victory in March.
Thursday’s race is a three-mile contest with level weights, compared to the four-and-a-quarter miles of the National, which is a handicap where the 40 runners carry different weights.
Clan Des Obeaux is a two-time King George VI Chase winner and Native River won the Cheltenham Gold Cup in 2018.
Rivals include this season’s King George runner-up Waiting Patiently, along with Aso, Mister Fisher, Clondaw Castle, Real Steel and 100-1 outsider Militarian.
Former champion hurdler Buveur D’Air, trained by Nicky Henderson, runs in the Aintree Hurdle after missing last month’s Cheltenham Festival.
Billaway, Cat Tiger and Dashing Perk are among the runners in the meeting’s first race over the National fences as amateur jockeys tackle the Foxhunters Chase.
The race is being run in the name of former Aintree chairman Rose Paterson, who took her own life last year.
On Saturday her husband, North Shropshire MP Owen Paterson, is launching the Rose Paterson Trust, a charity supporting suicide prevention projects.
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