Saturday's seven-race card is due to feature the November Handicap.
The going at Town Moor is currently described as heavy, soft in places.
An update on Thursday reported rain was already falling at dawn and is forecast to continue for the next 24 hours - and the inspection will take place at 8am on Friday.
Doncaster had to cancel day two of its previous Flat meeting at the end of last month, with the Group One Vertem Futurity Trophy transferred to Newcastle six days later.
Clerk of the course Roderick Duncan admits it will be "a struggle" for the fixture to survive.
"We're potentially forecast about 30 millimetres today and another four or five in the early hours of tomorrow," he told Sky Sports Racing.
"It's just a bit grim. We've got a lot of roads closed around the town. It's properly hitting Doncaster at the moment.
"We're going to struggle now. We've got to have a really positive forecast for Saturday morning and for all of Friday to give us much of a chance.
"If we can see a glimmer of hope we will have further inspections, but we'll need some positive changes in the way these forecasts are developing at the moment for Saturday to give us a chance.
"The monthly forecast has surpassed anything I've got on record. We're getting to the top levels for the whole of November now."
Doncaster had to cancel day two of its previous Flat meeting because of waterlogging at the end of last month, with the Group One Vertem Futurity Trophy transferred to Newcastle six days later.
