It had been thought that Dunwoody would be offered the ride but his agent, Robert Parsons, commented: "Richard hasn't been contacted and he has no mount in the race for the first time in many years."
Tony McCoy, who was also linked with Imperial Call, is to ride last year's runner-up, Challenger Du Luc.
Meanwhile, Michael Hourigan is still looking for a jockey for Dorans Pride, who runs in the Ericsson Chase at Leopardstown on Monday. Dunwoody has been the regular pilot for Dorans Pride but the former champion will be aboard Florida Pearl for Willie Mullins.
In the same day's Welsh National, bookmaker opinion is that Dom Samourai will avenge his 1997 defeat by Earth Summit.
In last year's race Nigel Twiston-Davies' gelding, the subsequent winner of the Grand National, fended off the thrust of Dom Samourai by a length and three-quarters, giving the Martin Pipe runner 13lb.
With that concession increased by 2lb - Earth Summit emerged as the new top-weight with 11st 10lb at yesterday's forfeit stage - layers favour Dom Samourai to turn things round.
With 21 acceptors left in yesterday for the pounds 50,000 handicap, the sponsors, Coral, price last season's runner-up as their 3-1 favourite, with Earth Summit second choice at 4-1.Reuse content