Novak Djokovic has split with Todd Martin, who had been acting as one of his coaches since the U.S. summer circuit last year.

Martin was brought on board to work on various aspects of the Serb's game, notably his serve, in tandem with Novak's long-time coach Marion Vajda.

But, as he prepared for the start of the European clay-court season here at the Monte Carlo Country Club, Djokovic revealed that the relationship has come to an end.

"Todd is a fantastic person," said Djokovic. "He has so much experience and was willing to share everything with me. There are no hard feelings but we just decided it was not working. It was probably a question of understanding what kind of person I am."

In other words, it was as much the cultural gulf which exists between American and Europeans as anything technical, although there were issues with the serve. "At the ATP Finals in London my shoulder was tired and the body automatically started to make adjustments because of that," Djokovic explained. "Then we tried a slightly different action and it all got very complicated. So now I am just going back to my original action."

More than most top players, Djokovic is known as a very emotional player who struggles to keep himself on track. "I am always fighting with my inner self," said the former Australian Open champion, who rose to No 2 in the world at the start of this year. "I am my biggest opponent. I am always thinking about things on court -- things about one's private life, everyday things. Sometimes I would prefer to be a little dumber, not to have so many things in my head."

Without suggesting that Martin is not emotional -- anyone who saw him reach the final of the US Open in 1999 would never accuse him of that -- it would be fair to say that he is a very different personality from the outwardly cocky and self-confident but inwardly uncertain Serb.

Word from the Djokovic camp emphasized that the breakdown in understanding between the two men was all about Europeans and Americans living in different worlds. "Speaking the same language -- and, as you know, Novak's English is excellent -- is not enough," an insider told me. "It's just the different way one expects to react to certain situations; how to approach problems. We all liked Todd but it just didn't work."

Djokovic, who is the top seed here at this ATP Masters Series 1000 event in the absence of Roger Federer, will continue to work with Vajda, a former Czech Davis Cup player, on a one-to-one basis.