Thursday's meeting at Fontwell is in serious doubt with several areas of the track waterlogged and more rain forecast.
Officials at the West Sussex track have called an 8am inspection on Wednesday and fear the worst.
"We have still got three or four areas that are waterlogged. We have seen some improvement in other areas of the course, but those areas have got worse if anything and it's been dry since Monday lunchtime," said clerk of the course Edward Arkell.
"If we are not going to be fit to race tomorrow there is more rain forecast from Wednesday afternoon onwards, so it is better we let everybody know and they can make alternative running plans. It's going to be a struggle."
Meanwhile officials at Musselburgh have called a precautionary inspection for 8am on Wednesday ahead of the meeting that afternoon. Ground conditions are described as good, but with a "tricky forecast".
Clerk of the course Harriet Graham tweeted: "Precautionary Inspection 8am due to forecast snow starting between 7-9am changing to sleet/rain later +3 Tricky forecast."
An 8am precautionary inspection has also been called for Wednesday's meeting at Thurles due to the uncertainty of the weather forecast.
A provisional all-chase card has been programmed by the British Horseracing Authority for Sandown on Friday in an attempt to safeguard the fixture. This will consist of the three chases originally scheduled plus three additional chase opportunities.
All additional races will be free to enter and a final decision on whether the existing hurdle races will be abandoned and the provisional chases activated will be made at 8am on Thursday.
Clerk of the course Andrew Cooper said: "Parts of the hurdle course are saturated. We are expecting further rain on Thursday, with some forecasts suggesting as much as 10mm. To give ourselves the best chance of staging a day's racing we have asked BHA to provisionally schedule an all-chase card ."
13 May 2013
Fabre confirms Ocovango for EpsomAspect on route to big things
Room at the top for Cityscape
Freedom steps into chasing ranks
Lucky thirteen in line for Lockinge
Galway beckons for Swinton hero
Sajjhaa set for late return
Cadeaux thriving in Singapore
Pink primed for Duke Of York
Liber takes aim at Musidora
Battle won for O'Brien
Pretending the real deal
Duntle back to winning ways
Classic glory for Flotilla
Style wins the day in Paris
Highclere double-handed for Dante
Cornerstone plans up in the air
Beckett planning Gesture workout
12 May 2013
No hurry for Jammy plansGuest in hunt for more Ascot glory
Vow set for Goodwood return
Gold-en boy Anodin in Classic hunt
Buick aiming for French strike
Angel flies home to land Chartwell
Barizan bounces back in style
Queally lights up Ascot meeting
Ektihaam storms to Buckhounds win
Nevis takes depleted Trial contest
Hard-fought battle won at Haydock
Secret impresses in Oaks Trial
Ascot drama for Fanning
11 May 2013
Felix foot-perfect on fencing debutCavalryman leads Cup charge
Ramsa ready to stand Trial
Duntle out to dazzle in Amethyst
Swift return doesn't bother Moran
Garman gives Bolger hope
Henderson: Ground vital for Voice
McMahon sweet on Tart Ascot claims
Murphy to move to France
Athos flies to Ormonde glory
Dee day for impressive Magician
Kingdom confirmed for Queen Anne
Secret's out for Lingfield glory
Lambe expects good run from Hall
Marengo ready to do battle
Greatwood on trial at Lingfield
Barizan sneaks into Swinton
Jamesie gunning for Vic-tory
10 May 2013
Telescope focus is on DanteBlinkers considered for Guarantee#
Bonfire camp bemoan Huxley flop
Moohaajim has six appeal
Ascot welcomes a couple of Guests