Elena Rybakina was forced to retire from her quarter-final against Iga Swiatek at the Cincinnati Open due to an ankle injury.

The No 2-ranked Rybakina was trailing 4-1 when she took a medical timeout to have trainers address her left ankle and retired from the match moments later.

With top seed Aryna Sabalenka losing to Sara Bejlek, the 27-year-old Rybakina could have risen to No 1 in the rankings by reaching the final.

Swiatek, the defending champion, has reached at least the semi-finals in each of her last four appearances in Cincinnati.

"Not the way you want the match to end," Swiatek said. "She didn't look good, obviously. Then she wanted treatment and I wasn't sure if she was going to be back or not.

"She is walking normally now. I felt really sorry for her but hopefully it's nothing serious and she is going to be ready for the US Open."

Swiatek beat Rybakina in the semi-finals in Cincinnati last year but this time will face American Jessica Pegula in the last four.

World No 3 Pegula came through a fightback from Amanda Anisimova to claim a ‌6-4 2-6 7-6(4) victory.

In the men's draw, seventh seed Flavio Cobolli made up for a poor start to beat American ​Tommy Paul 2-6 6-3 6-4 and reach his first ATP Masters ‌1000 semi-final.

He will play Arthur Fils for a place in the final after he defeated Argentina's Thiago Agustin Tirante 6-3 6-2.

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