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 ."
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