Llewellyn, whose left leg was broken when kicked by a horse at Ascot last week, has been told by the Jockey Club's chief medical officer, Michael Turner, that he will not allow him to ride in the race using a splint.
'The Jockey Club rang me this afternoon to say that to pass a medical I would have to stand on tiptoes on my broken leg and that I would not be able to wear a splint,' Llewellyn said. 'It would be foolish to ride without a splint and it is impossible to stand on my tiptoes without support.
'It seems the Jockey Club are not happy for me to ride but I respect their decision and am not bitter about it.'
Llewellyn, stable-jockey to Nigel Twiston-Davies, had hoped he would able to make it to Aintree having yesterday ridden out for the trainer without any distress.
David Pipe, the Jockey Club's spokesman, said: 'I'm pleased he has made the decision. It is up to him, but it is a matter of his own safety as well as the safety of the other jockeys. Michael Turner is perfectly fair on these occasions. He passed Carl to ride in the Grand National last year only 10 days after he had broken his collar-bone.'
Bridgwater, who lost the ride on Captain Dibble to Peter Scudamore just before last year's National, has been confirmed as the rider of Young Hustler who is a 10-1 chance.
First Trump's participation in the 2,000 Guineas on 30 April is in doubt. 'He has strained a ligament,' his trainer, Geoff Wragg, said. 'He will miss the Free Handicap, which was his target, and is very doubtful for the Guineas because I don't know when I will be able to work him.'
Martin Pipe registered his 100th winner of the season with Luv-U-Frank at Ascot yesterday. He reached the same landmark on 25 January last term.
Aidan O'Brien, trainer of Minella Lad, has failed in his appeal to have the horse promoted to second, ahead of Avro Anson, who accidently interfered with him in last month's Stayers' Hurdle at Cheltenham.
Animal-rights demonstrators delayed last night's final of greyhound racing's BBC Television Trophy at Sunderland. The race was won by the 2-1 chance Jubilee Rebecca.
Obituary of the racing journalist Peter Scott, page 16