The Philip Hobbs-trained gelding, who is currently the 7-2 market leader with Paddy Power and Cashmans, is usually partnered by stable jockey Richard Johnson.
However, he is sidelined for as long as three weeks with a pelvic problem, leaving Dobbin to take the ride on the seven-year-old.
Monkerhostin warmed up for the Grade Three contest with a win at Stratford last month.
He has proved a popular choice with punters as his rating over fences is far inferior to his mark over hurdles and also due to the fact he will carry a feather-weight 10st.
Dobbin will not be a total stranger to Monkerhostin, however, as he has partnered the horse previously, the pair finishing second to Flame Creek in an intermediate hurdle at Kelso in May 2002.
In other jockey news, Gary Moore has booked Leighton Aspell to ride his 9-1 shot Tikram.
The seven-year-old’s usual partners Timmy Murphy and Jamie Moore are both committed to riding Martin Pipe’s runners in the race, leaving Moore searching for a rider.
However, Aspell is set to renew his acquaintance with Tikram, a horse he has ridden three times before.
“Leighton rode the horse when he was third in the Tote Gold Trophy and he knows him well which is always a useful advantage. Leighton is a very good rider,” said Moore.
: 7-2 Monkerhostin, 11-2 Thisthatandtother, 9-1 Farmer Jack, Fondmort, 10-1 Tikram, Ollie Magern, 12-1 Celestial Gold, 14-1 Le Duc, Ground Ball, 16-1 Colca Canyon, Kelrev, It Takes Time, Take The Stand, 25-1 Atum Re, Better Days, 33-1 Ballycassidy, Simply Gifted.
: 7/2 Monkerhostin, 6/1 Thisthatandtother, 7/1 Farmer Jack, 8/1 Fondmort, 10/1 Tikram, 12/1 Celestial Gold.