World number two Rybakina was forced to retire due to a left ankle injury when trailing 1-4 in the opening set of her clash with Swiatek on Thursday evening.
The issue appeared to surface during a point Rybakina lost when she was serving at 1-4, 40-15.
Play was stopped as Rybakina had a mid-game medical evaluation, and the 26-year-old Kazakh then determined that she was unable to continue.
“Of course, now I feel not the greatest, I couldn’t even push from the serve,” the two-time Grand Slam champion said afterwards. “It’s painful to walk, and we will know more tomorrow when I do the MRI.
“It’s been bothering me for a long period of time. It was under control, but then after playing a lot of matches in Canada and coming here playing two matches in a row. The match against [Magdalena] Frech stopping with the rain delays, I started to feel it more, and I took a day off completely after.
“It was feeling okay before the match, but unfortunately one wrong movement, one landing, and something happened.”
World No 5 Swiatek gave her reaction to Rybakina’s retirement and admitted she had been “scared.”
“Honestly, I felt a bit, like, scared because I don’t know if I see a player having an injury like that,” said the 25-year-old Pole.
“I wasn’t sure because she didn’t look good, obviously. But then she wanted a treatment, so I wasn’t sure if she’s going to be back or not.
“So, I wanted to be really focused on just being ready because breaks like that can really throw you off of your rhythm and the momentum. But then I felt really sorry for her, but hopefully it’s nothing serious.
“I was feeling anxious just looking at this situation. I hope Elena will be fine. The next tournament is the priority. I know this one is important as well. But US Open is US Open. I hope she’s gonna be ready for that.
“She’s super close to being No 1 in the world. It’s a shame. I thought we were playing a good match. But health is a priority. I hope she’s gonna be okay.”
Swiatek is on a 10-match winning streak and is aiming to win consecutive WTA 1000 titles following her victory at the Canadian Open. The six-time major champion is also trying to secure back-to-back titles in Cincinnati.
Waiting for Swiatek in the final four is Jessica Pegula. The third seed defeated fellow American Amanda Anisimova 4-6, 6-2, 7-6(4) to book her spot in Saturday’s semifinal.
