A foot injury forced former US Open champion Emma Raducanu to retire from her Korea Open quarter-final clash with top seed Daria Kasatkina after losing the first set 6-1 on Saturday.

Britain's Raducanu struggled to serve with her injured left foot, her landing leg, as she played on after a medical timeout, committing a double fault and not chasing returns across the court.

The foot injury also surfaced during 21-year-old Raducanu's round of 16 clash with Yuan Yue, where she was able to continue after a medical timeout and win 6-4 6-3.

"I feel sorry for Emma ... it's a pity to get injured, especially in the deeper stages on the tournament," Kasatkina said after the match. "I wish her a speedy recovery."

Raducanu's latest setback comes after she was dumped out of the US Open in the first round by Sofia Kenin last month after opting not to play any tournaments in the weeks leading up to it.

Kasatkina will play fellow Russian Diana Shnaider in the semi-finals later on Saturday, after rain washed out Friday's play in Seoul.

Fourth seed Shnaider beat Australian Open quarter-finalist and Ukrainian fifth seed Marta Kostyuk 7-6(7) 6-3 in the quarter-finals.

Brazilian third seed Beatriz Haddad Maia faces former French Open quarter-finalist Veronika Kudermetova in the other semi-final, after brushing aside Veronika's sister Polina Kudermetova 6-2 6-1 in the last eight.

Russia's Veronika beat Viktoriya Tomova 7-5 6-3 to reach her first semi-final of the year.