Wimbledon champion Roger Federer has split with his coach after the most successful year of his career.
Federer and Lundgren celebrate the Wimbledon win
The shock announcement comes just three weeks after Federer thrashed Andre Agassi to win the season-ending Masters Cup.
Federer and Sweden's Peter Lundgren were considered inseparable after teaming up in 1998.
But the Swiss star, 22, claims he needs a "new impetus", although he insisted he had not lined up a replacement.
"This decision comes after a lot of hard thinking," Federer said.
"I felt as if I'd fallen into sort of the same old routine and over the last few months our relationship has become more strained."
Federer told Lundgren of his decision last week.
"It wasn't easy and of course Peter was very disappointed," said Federer, who won more prize money in 2003 than any other player and finished second in the rankings behind American Andy Roddick.
Federer also won the Wimbledon title in July, beating Mark Philippoussis 7-6 6-2 7-6 in the final after overcoming Roddick 7-6 6-3 6-3 in the semis.
Federer has denied reports in Switzerland that he will replace Lundgren with former Olympic singles champion and compatriot Marc Rosset.
"I've never even considered that option," said Federer, adding that
he was unconcerned about playing next month's Australian Open
without a coach.
"I am hoping to find a coach capable of introducing me to new ideas. We will have to have the same approach to the game," he added.