Slovakia's Dominika Cibulkova withdrew from her semifinal match against France's Marion Bartoli at the Bank of the West Classic on Saturday with a left abdominal strain.
"It has been bothering me on and off the whole week," Cibulkova said. "It was painful when I played Marina (Erakovic) but I was able to get through that match. I thought it would be better in the morning but I saw a doctor and he recommended not playing since the injury could worsen."
Cibulkova had the same problem earlier in the year, missing two tournaments after getting through the quarterfinal at Madrid.
"Maybe I rushed to play too quick," she said. "I don't want to make the same mistake."
Cibulkova still plans to travel to San Diego, where she is scheduled to play Wednesday.
"It's still open and I'm hoping to be ready," she said. "I still have things to do in San Diego."
The 19th-ranked Cibulkova is projected to rise to No. 16 in the WTA singles rankings by reaching the semifinal. She beat qualifier Marina Erakovic in the quarterfinals Friday, 6-1, 6-1.
"It was a great tournament for me," Cibulkova said. "I was looking forward to maybe winning my first tournament. I was so full of confidence."
The ninth-ranked Bartoli reached her fourth final of the year and her third final at Stanford. She won the title in 2009.
Bartoli reached the semis when Japan's Ayumi Morita withdrew with an injury after the first set Friday night.
"This has never happened to me but there's not much I can do about it," Bartoli said. "It's a shame Dominika had to be put out. It will be an extremely tough match tomorrow and I need to get ready."
Bartoli is the lone seeded player left in the main draw and will meet Serena Williams in the championship match on Sunday.
Both singles players addressed the crowd and Bartoli hit balls with several kids before giving way to the scheduled semifinal doubles match.