The top seed had been due to meet 17-year-old American Amanda Anisimova for a spot in the semi-finals, a match that will now take place on Thursday.
And the wet conditions are likely to benefit Halep, said three-times champion Mats Wilander.
"There is a lot of pressure on Simona Halep in this one," said Wilander, in Paris as expert pundit for Eurosport.
"Amanda Anisimova is an excellent ball-striker. However, I feel the heavy conditions will make it tough for her to hit through the ball to Halep because she defends so well. Obviously no one wants rain, but the conditions could help Halep."
The remaining quarter-final pits American Madison Keys against Australian Ashleigh Barty.
Britain's Jo Konta and Marketa Vondrousova reached the last four on Tuesday and thanks to Wednesday's washout, they will enjoy an extra day's rest before contesting their semi-final on Friday.
(Editing by Pritha Sarkar)
