Muguruza and Sumyk have worked together for the past four years, taking in her breakout triumph at the 2016 French Open where she beat Serena Williams in the final in straight sets.
The 25-year-old won Wimbledon in 2017 - Venus Williams her victim on that occasion - and reached world number one, although her Wimbledon success came predominantly under the guidance of Conchita Martinez as Sumyk attended the birth of his daughter.
The pair were involved in a pair of high-profile courtside rows at the WTA Elite Trophy last year and Muguruza's fortunes have been on the wane – culminating in a first-round exit at the All England club last week versus Brazil's Beatriz Haddad Maia.
"Few words to announce the end of an extraordinary ride," Muguruza tweeted.
"2 Grand Slams and World No 1. Beyond grateful for this last 4 years. Merci Sam."
Muguruza won this year's Monterrey Open when former Sumyk pupil Victoria Azarenka withdrew during the second set of the final but her world ranking has tumbled to 27.