Exeter's meeting on Sunday is now subject to an 8am inspection on raceday morning.
Officials at the Devon circuit had intended to assess conditions at 8am on Saturday, but that has now been put back 24 hours.
Although the track was raceable on Friday morning, 18 millimetres of overnight rain fell - on top of 87mm over the last four days.
An ominous forecast on Saturday is also giving cause for concern.
Exeter clerk of the course Barry Johnson said: "We'd be fine tomorrow, so it's pointless inspecting on Saturday morning.
"We are worried about a band of rain later on Saturday - we could see 40mm - but, at this moment in time, I'd be quietly confident we'd be OK.
"The course is taking the rain fantastically well."