Stefanos Tsitsipas has brought his father Apostolos back as coach after ending his brief partnership with Goran Ivanisevic, the former world number three said.
Tsitsipas, 26, ended his collaboration with Ivanisevic, who helped Novak Djokovic claim nine of his 24 Grand Slam titles, last week after less than two months.
Tsitsipas, the 2021 French Open and 2023 Australian Open runner-up, has tumbled to 30th in the world rankings and has failed to get beyond the second round in the first three Grand Slams of the season.
Following Tsitsipas' first-round exit at Wimbledon, Ivanisevic delivered a scathing assessment of the Greek, saying he had "never seen a more unprepared player" in his life.
His title win in Dubai in February is the only final he has reached in 2025.
"Some journeys have a way of circling back to where they began," Tsitsipas, who lost to Christopher O'Connell in the second round of the Canadian Open on Wednesday, posted on social media.
"After some time apart, I've reunited with the person who first believed in me - my father.
"I'm grateful to share the court and the road ahead with him once again. We've been through every chapter of this journey together, and this next one feels right.
"Sometimes, coming home is the boldest step forward."