Swan came into Saturday on a eight-match winning streakBritain's Katie Swan was forced to retire from her maiden WTA semi-final in Chennai because of illness.
Swan was trailing 3-0 to third seed Magda Linette of Poland after 16 minutes of their match when she called for a medical timeout.
After being assessed by medics, Swan was not well enough to resume.
The British number six had only finished her quarter-final at 3am on Saturday - a match where she also needed a medical timeout.
"I feel bad for Katie," Linette said afterwards. "She gave everything yesterday and it looks like she has paid the price today."
The world number 67 will face Czech teenager Linda Fruhvirtova in the final after the 17-year-old defeated the 2020 French Open semi-finalist Nadia Podoroska of Argentina 5-7 6-2 6-4.
However, Swan's performance this week has already ensured that she will move inside the world's top 150 when the new WTA rankings are published.
