Numbers in the major steeplechase and hurdles races this year have already been light but suggestions the Riccarton track could be very heavy coupled with other timing issues has Mills fearing for the iconic races.
"A few days ago I was really worried we could lose them which is why we have asked trainers to give us a idea of what horses they are bringing," says Mills.
"There are a few factors causing the numbers shortage. Obviously we don't have local jumpers down here any more, which even in recent years were good for one or two more horses per race.
"Then we have had a lot of rain and I am sure some of the northern trainers think the track has been under a foot of water but it hasn't been that bad.
"Yes, it will be true winter footing but the track is in good condition.
"And there has been a general shortage of horses in the open jumps races which doesn't help when they have to travel."
Some of the big-name jumpers like The Cossack (in Australia) and Nedwin (setback) will miss the carnival and a regular Grand National supporter like trainer Paul Nelson having The Cossack racing at Sandown on Sunday it makes travel to Riccarton more taxing.
Entries for the Saturday's jumps races close at noon on Tuesday and Mill says the CJC will run races like the two Grand Nationals with six or even five horses but would obviously like more.
Last year the Grand National Steeplechase attracted nine horses and was won by one of New Zealand's greatest ever jumpers, the now-retired Tallyho Twinkletoe.
As wet as the Riccarton track is certain to be its workload for the week will be lessened by the flat races at next Wednesday's GN Hurdle meeting being held on the synthetic track inside the main track in what will be a first for New Zealand racing.