Doncaster will need a "minor miracle" for its Flat finale to go ahead on Saturday after the course was hit by more than an inch of rain on Thursday.
Clerk of the course Roderick Duncan changed the ground to heavy, waterlogged and standing water in places, on Thursday after a band of rain parked itself on top of the town rather than skirting north.
An inspection will take place at 8am on Friday to determine whether the fixture can take place on Saturday, when the November Handicap is the feature contest, with adverse weather forecasts for the weekend as big a factor as the underfoot conditions.
The BHA is looking at contingency options, such as some of the races being staged at another track, but this is complicated by the six-day break in Flat racing that follows Doncaster's finale.
"We've had 27mm of rain today, which is a little bit more than we were expecting," said Duncan on Thursday. "It's forecast to continue raining heavily until 2am.
"There's a possibility of further rain on Friday and Saturday, so I will have to see how it develops and assess the possibility of the ground drying out enough to allow for more rain on the day.
"If the forecast is still for significant rain then we'll make a decision on Friday morning. If there's an improvement we may have another look later in the day but I think we'll need a minor miracle – we're having a month's worth of rainfall in one day."
A Met Office amber warning was issued for the area between 6am on Thursday and 6am on Friday, with a high risk of flooding.
Doncaster was forced to cancel last month's Group 1 Vertem Futurity Trophy meeting due to waterlogging, although the feature contest was saved and run at Newcastle, making it the first top-level race to be run on a synthetic surface in Britain.
“We've been in regular communication with Doncaster," said BHA spokesman Robin Mounsey. "First and foremost our fingers are crossed that Saturday’s fixture can go ahead. We're aware that the racecourse is giving the fixture every chance.
“As is standard practice, we look at possible contingency options should major fixtures or races be abandoned, although this is made more complicated by the fact the fixture marks the end of the Flat turf season.”