World number one Iga Swiatek is looking for a new coach after splitting with Tomasz Wiktorowski following three seasons working together.
Wiktorowski, 43, joined Swiatek's team as coach in 2022 when she had one Grand Slam success to her name.
The Pole helped Swiatek to four further Grand Slam titles, including three successive French Opens.
She became the first Polish player to reach world number one in April 2022 and has spent a total of 123 weeks at the top of the rankings.
"After three years of the greatest achievements in my career, together with my coach Tomasz Wiktorowski we decided to part ways. I want to start with a big thank you and appreciating our work together," Swiatek wrote on Instagram.
"His experience, analytical and strategic attitude and enormous knowledge about tennis helped us to achieve things I've never dreamed of only a few months after we started working together."
Swiatek says she has held "first talks" with prospective new coaches and will take a "couple of weeks" to start work with her next appointment.
She is not playing at the ongoing China Open, having withdrawn beforehand because of "personal matters".
The 23-year-old won the French Open and US Open during her opening season with Wiktorowski.
During 2022, Swiatek embarked on a 37-match winning run - the longest streak by a woman this century.
The Pole won a fifth Grand Slam - her fourth with Wiktorowski - at Roland Garros in June.
But Swiatek was disappointed with her hard-court performances this season, exiting the Australian Open in the third round and the US Open at the quarter-final stage.