Johanna Konta's bid to reach the French Open final will start at 10:00 BST on Friday after organisers had to change the schedule because of expected rain.
The British number one, 28, will meet Czech teenager Marketa Vondrousova on Court Simonne Mathieu.
All three Roland Garros show courts will be used in a bid to complete the matches before heavy rain hits Paris.
Roger Federer and Rafael Nadal will start their men's semi-final on Court Philippe Chatrier at 11:50 BST.
The other women's semi-final between Ashleigh Barty and Amanda Anisimova will be on Court Suzanne Lenglen at 10:00.
Konta's semi-final was originally scheduled for Thursday, but was pushed back after downpours on Wednesday meant no play was possible.
That meant the remaining quarter-finals matches could not be played and were rescheduled for Thursday.
However, more disruption is expected on Friday with rain showers forecast for late morning and through the afternoon.
Men's final on Monday?
Tournament director Guy Forget said further delays could see Saturday's women's final moved back to Sunday, with the men's final switching to Monday.
"It's not what we hope, but if we have no other choice, then that's what we will do," he said.
"When we have uncertain weather, of course; it's very hard to predict scheduling.
"We have to always study the worst-case scenario, knowing that ideally we want to try to finish on Sunday."
The newly rebuilt Chatrier, with a capacity of 15,000, is Roland Garros' main court.
The 10,000-seater Lenglen is the second show court, with the 5,000-seater Mathieu, a semi-sunken court surrounded by four greenhouses, opened this year as the third.