Romanian tennis player Simona Halep, world No.
1, on Thursday advanced to the quarterfinals of the Italian Open, a WTA clay court tournament held in Rome, as American Madison Keys had to retire with a right rib injury.
The 2017 Italian Open finalist is set to play either France's Caroline Garcia or American Sloane Stephens, reports Efe.
"I am really sorry I have to withdraw from this year's Internazionali BNL d'Italia, " Keys said in a statement.
"I felt my rib in my match yesterday and after trying to warm up this morning it will still painful.
I look forward to returning to this great event next year and seeing all my fans in Rome. "
Halep had started her 2018 Italian Open campaign on Wednesday by routing Japanese Naomi Osaka 6 - 1, 6 - 0.
The 26 - year - old Halep seeks her seventh clay court title, following the Hungarian Open, Nuremberg Cup (2013), Bucharest Open (2014, 2016) and Madrid Open (2016, 2017).