Belinda Bencic has withdrawn from the Western & Southern Open with a right forearm injury, shortly after losing the first set of her third round encounter against Lucie Safarova.
The 18-year-old Bencic upset a string of seeds, including world number one Serena Williams, to win the Rogers Cup in Toronto last week.
Following her withdrawal on Thursday, the Swiss player said that she was not particularly concerned about the injury. I don't think it's very serious," Bencic said.
"I wasn't 100 per cent, and to beat Lucie or even compete against her, you have to be 100 per cent. I didn't want to retire. This was the first I've ever had to retire. I hope it gets better.
"Every match, it was getting tighter and tighter. I was hoping that a lot of (therapy) would help, but I couldn't do it.
"Physically I'm fine except this, and mentally I'm also fine. I mean, I won a lot of matches. I think that's the best that can happen to you mentally."
Safarova will take on the winner of the match between 14th seed Elina Svitolina and unseeded Caroline Garcia in the quarter-finals.