Some of Australia's prime wheat growing areas in central and northern New South Wales and southern Queensland suffered drenching rains this week on crops still in the field.
The rain could cost producers millions if it causes the wheat to be downgraded from hard milling to feed grade.
"I'm not confident the quality is going to hold up," said Keith Perrett, chairman of the government's National Rural Advisory Council.
"Given we've had the rain, the muggy weather, it's probably not looking that good.
"The critical timing is the next couple of days; if we can get some hot, fine weather, it will lessen the chances of damage."
Harvest of what looked to be a bumper crop has been brought to a standstill this month by widespread rains.
Mark Irwin, managing director of GrainCorp, says he is expecting to see grades come off from where they were a week ago, but not as much as many people are expecting.
"You might lose a little bit in terms of tons, the quality might come off a little bit," Mr Irwin said.
"But there's still pretty good quality wheat up there.
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