Haydock's meeting on Sunday is subject to a 2pm course inspection on Saturday.
The Merseyside circuit is currently raceable, but 20 millimetres of rain has been forecast heading into the weekend.
With 8mm of rain having fallen on St Stephen's Day, the going is officially described as heavy.
Clerk of the course Kirkland Tellwright said: "Whether we race or not is finely balanced at this stage.
"We had seven millimetres overnight and are forecast another 20.
"The merit of calling a Saturday inspection is we get to see more hands unfold before we play our own.
"We got through last Saturday's meeting fine but that could have prejudiced Sunday's chances.
"I'd say it's a 50-50 chance at present."