(CNN)Sometimes it can pay off to have a tennis legend in your coaching corner, but sometimes things just don't work out.
Martina Navratilova ends coaching role with Agnieszka Radwanska
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When Agnieszka Radwanska announced in December that she had hired her idol Martina Navratilova, it seemed the Polish player was taking a significant step in her bid to win a first grand slam title.
Instead, they have parted ways just months into the 2015 season, with the former world No. 2 having slumped from sixth in the rankings to ninth -- reaching only one semifinal, and that in a minor tournament in her home country.
Navratilova, an 18-time grand slam singles title winner, said in a statement that she was too busy to continue in her part-time role.
Born in the former Czechoslovakia but a longtime U.S. citizen, Navratilova married her partner Julia Lemigova in December.
"I think I underestimated the time it would take to make this a proper and good situation for both Agnieszka and me," the 58-year-old said on the WTA Tour website.
"I have quite a busy family life now as well as my TV work and other business commitments, which all combined make it impossible to dedicate the amount of time necessary to do a great job.
"Tomas Wiktorowski, Agnieszka's full-time coach, certainly knows what he is doing and he will be able to continue to build on some of the adjustments we were trying to make. I really enjoyed working with Aga and her whole team and I wish her all the best for the rest of the season."
Navratilova's appointment last year followed a recent tennis trend, particularly in the men's game, of top players hiring former grand slam winners.
No. 1 Novak Djokovic hired Boris Becker, Roger Federer works with Stefan Edberg, while Andy Murray was transformed into a champion by Ivan Lendl before the Scot switched to Amelie Mauresmo.
Goran Ivanisevic helped fellow Croatian Marin Cilic win the 2014 U.S. Open, while Michael Chang has guided Kei Nishikori from being Japan's promising star to a genuine title contender -- reaching the New York final in September and reaching a career-high fourth in the rankings in March 2015.
Radwanska has not fared so well. She lost her opening match of the clay event in Stuttgart this week, beaten by 15th-ranked Italian Sara Errani.
"I just wanted to thank Martina for her time and efforts over these last few months," the 25-year-old said on her social media accounts.
"It was a great experience to work with one of the all-time greats. However, we both agreed that as Martina could not commit 100% to the project then it was not going to work as a long-term partnership.
"We will stay friends and I wish her all the best in her personal and professional life."
Meanwhile, former world No. 1 Caroline Wozniacki reached the final in Stuttgart after beating Romanian second seed Simona Halep 7-5 5-7 6-2 in Saturday's opening semi in Germany.
The Dane next faces home hope Angelique Kerber, who beat defending champion Maria Sharapova in round two.
The German world No. 14 reached her second successive WTA Tour final -- having claimed the Charleston title on April 6 -- after winning 6-3 6-1 against 43rd-ranked American Madison Brengle, who eliminated Wimbledon champion Petra Kvitova earlier in the week.
In Spain, top seed Nishikori reached the final of the Barcelona Open with a 6-1 6-2 victory over Slovakian Martin Klizan on Saturday.
The defending champion will next play Pablo Andujar. who beat four-time runner-up and fellow Spaniard David Ferrer 7-6 (8-6) 6-3.