Third-seeded Madison Keys pulled out of the Generali Ladies due to illness on Saturday, hours before her semifinal against Viktorija Golubic of Switzerland.
Tournament organizers say the seventh-ranked American has a cold.
Golubic is advancing to her second career final after winning the event in Gstaad in July.
On Friday, the 62nd-ranked Golubic won her quarterfinal against top-seeded Garbine Muguruza after the French Open champion sprained her left ankle and retired at 4-4 in the final set.
In Sunday's final, Golubic will face either No. 20-seeded Dominika Cibulkova of Slovakia or No. 4 Carla Suarez Navarro of Spain.