British number one Johanna Konta has parted company with coach Michael Joyce after less than a year together.
The 27-year-old began the year as a top 10 player, but is now 45th after struggling at the Grand Slams in 2018.
Konta is playing in Moscow next week and hopes to have a new coach in place in time for pre-season training.
American Joyce was Konta’s third coach in as many years, joining her after she had worked with Esteban Carril and Wim Fissette.
Konta reached the second round at the Australian Open and Wimbledon, and went out at the first-round stage of the French Open and US Open.
She made it to the final of the Nottingham Open in June, her only final of the year, but has not been beyond the second round of her past six tournaments.
Joyce spent six years as part of Maria Sharapova’s team, the Russian winning the US Open and the Australian Open as well as becoming world number one while the pair worked together.
BBC tennis correspondent Russell Fuller
Konta’s ranking has fallen from nine to 45 in 2018. There have been some solid results on tour, but only two matches won at Grand Slams – which is a poor return for a player who had reached a Grand Slam semi-final in each of the two previous years.
And so, for the third year in a row, Konta has decided to make a change. At 27, can she find someone who might take her out of her comfort zone in order to compete again with the world’s top 10?
Konta will play her final event of the year in Moscow next week and hopes to have a new coach in position in time for winter training.
She has also moved management companies, and is now with StarWing Sports, which has enjoyed success with Stan Wawrinka and signed Kyle Edmund this time last year.
Since the agency paired Edmund with Freddie Rosengren and Mark Hilton, the British number one has reached the semi-finals of the Australian Open and a career-high ranking of 14.