British number one Laura Robson has been accused of lacking maturity and commitment by her former coach Zeljko Krajan.
The 19-year-old linked up with the Croatian after the Olympics last year and the partnership appeared to be flourishing as she defeated Kim Clijsters and Li Na to reach the fourth round of the US Open.
But Krajan, who guided Dinara Safina to world number one and is renowned as a hard taskmaster, was not a natural fit with the laid-back Robson and it emerged this week the pair had parted ways.
Krajan told The Times: "The mentality is different. I did expect more from Laura but when it doesn't go that way any more it is not the time to stay.
"She was not mature enough to do this kind of work enough times for me. She needed to be more serious and to commit herself more.
"She had to do this every day, not only in the big tournaments."
The 19-year-old has continued to climb the rankings this season and, at number 41, is within sight of being seeded at the French Open later this month.
But there have been poor results, too, with six first-round defeats on the WTA Tour and the disappointment of Great Britain's failure to reach the Fed Cup World Group.
Robson sealed her first win over a top-five player on Monday, beating Agnieszka Radwanska in the second round of the Madrid Open, but last night was beaten by former world number one Ana Ivanovic.