Sunday's Welsh Grand National meeting at Chepstow has been called off after an inspection because of heavy rain.
The course is already waterlogged and more rain was forecast to fall before the big race.
The meeting has been rescheduled for Saturday, 9 January.
Heavy rain has also caused the postponement of both days of the Christmas fixture at Wetherby. Saturday's card was scheduled to feature the Rowland Meyrick Chase.
Chepstow's clerk of the course Keith Ottesen said: "There was every chance this was going to happen and we have done it before. Details of entries will be released in due course.
"It's due to be a drizzly day on Saturday and then another band of rain is forecast to move through with rain from midnight until virtually 12:00 on Sunday which would give us another 8-10mm, which we just can't take."
The Castleford Chase was Sunday's main race at Wetherby.
"We've had 32 millimetres of rain since Friday lunchtime," said clerk of the course Jonjo Sanderson.
"The dykes down the back straight have flooded so that is our problem, not waterlogging.
"It's forecast to continue raining on Saturday, so it's not going to improve."