Leading owners Gigginstown House Stud are set to have three runners in the Crabbie's Grand National at Aintree on Saturday,
Retained rider Bryan Cooper will have the choice of First Lieutenant, Rule The World and Sir Des Champs in the world's greatest steeplechase.
Gigginstown Stud manager Eddie O'Leary said: "Bryan will ride one, David Mullins will ride another and we'll see who is available to ride the third horse."
Nina Carberry is not expecting to have a ride if Knock House fails to make the cut.
Carberry, who has completed the National course on four of her five rides, has partnered Mick Channon's chaser twice this season, winning at Cheltenham in November and finishing fourth in the Kim Muir last month.
However, he currently need two horses above him in the list to come out to get a run.
Carberry said: "Hopefully I'll ride him (Knock House) if he gets in. You never know how they'll take to it until they go, so we'll see."
Tom Scudamore is keeping his fingers crossed he has made the right decision by siding with Ballynagour.
The leading jockey, who has not been seen in competitive action since suffering a heavy fall at Uttoxeter on March 19, will make his comeback at Aintree on Thursday, when his rides include Betfred Bowl outsider Dynaste.
Scudamore is set for a big afternoon on National day, when he will reunited with brilliant World Hurdle hero Thistlecrack in the Liverpool Stayers' Hurdle before getting the leg-up on David Pipe's Ballynagour in the National.
"I'm not going to have any rides before Aintree, but I'm feeling great and can't wait to get back," said the jockey.
"I'm riding Dynaste on Thursday, but it'll be a fairly quiet day and then it will be all systems go for Friday and Saturday."
Scudamore has chosen Ballynagour over two other Pond House inmates in Soll (Conor O'Farrell), who has completed in two previous Nationals, and Vieux Lion Rouge (James Reveley).
He said: "It was a very tough decision as all three have a similar chance. Soll loves it round there, but is higher in the weights now, while Vieux Lion Rouge is an improving young horse.
"I went for Ballynagour as he has some very strong form with the likes of Cue Card and Silviniaco Conti and his run at Cheltenham suggested he is coming back to form."