Victoria Azarenka withdrew from the Doha Open Friday ahead of her semi-final clash with Garbine Muguruza, blaming an injury the effects of which could be seen as she battled through her last-eight tie against Elina Svitolina.
"I am very sorry to have to let you know that I have to withdraw from the semi-final here in Doha tonight," Azarenka said in a statement.
"Unfortunately, the pain in my back that I experienced during (Thursday's) match has not gone away enough in order for me to be able to compete tonight."
Azarenka, a two-time winner of the Australian Open in 2012 and 2013, reached the quarters by seeing off Ukrainian top seed Svitolina, 6-2, 6-4.
But back pain dogged her effort and she visibly slowed during the second set.
"The pain didn't really get any better. I'm pretty proud of the way I handled it mentally. I tried to approach it and focus on the things that I could do rather than the things that I couldn't do," she said after the match.
Muguruza will face either Petra Kvitova or Jessica Pegula in the final Saturday depending on the outcome of their semi-final clash.