Mark Philippoussis is no longer helping to coach world No 5 Stefanos Tsitsipas, the Australian former tennis star said, calling it the end of "a great ride".
Philippoussis joined Tsitsipas's father Apostolos in the coaches box in the second half of last season and helped guide the Greek player to the Australian Open final.
Tsitsipas, who was beaten in the final in January by Novak Djokovic, previously hailed the impact of "wise man" Philippoussis.
But the 46-year-old Philippoussis, a former Wimbledon and US Open finalist of Greek heritage, wrote on Instagram that the partnership is over, days before the French Open.
He did not say why.
"Thanks for the opportunity of being a part of your team," Philippoussis said on Tuesday.
"It was a great ride and experience, and I'm proud of what we achieved together in the short amount of time we had.
"I wish you health, happiness and success for your future, on and off the court!"
Tsitsipas's father remains his main coach.