ROGER FEDERER, pictured, has come out in support of Andy Murray's call for more stringent drug testing in tennis.

The 17-time major winner believes the tour should step up testing so that the sport does not find itself mired in a crisis.

"I feel I am being tested less now than six or seven years ago and I do not know the exact reasons why we are being tested less," he said yesterday at the O2 Arena where he will this week defend his Barclays ATP World Tour Finals title.

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Murray has been outspoken about what he believes to be too few blood tests for players, particularly out of competition.

"I agree with Andy," said Federer. "We do not do a lot of blood-testing during the year, I just think it is important to have enough tests out there. I do not like it when I am only being tested whatever number it is, which I do not think is enough, I do not think it's sufficient during the year."

He called for an increase in tests, adding: "It is clear and vital that the sport stays clean, it has got to. We have had a good history in terms of that and we want to ensure it stays that way."

Federer, who has won the tour finals on six occasions, comes to London determined to make more history. He is resigned to losing the world No.1 spot to Novak Djokovic this morning.

The Serb, who also last night supported Murray's stance on drug-testing, will retain this status as best player in the world whatever happens at the O2.

However, it was typical of Federer, at 31, not to give up on hopes of becoming world No.1 again. When asked how realistic this ambition was, he replied: "We'll see. I obviously gave it everything I had last year. This is a full-on process that obviously takes a lot of sacrifice."

He confirmed he was playing a schedule for next season that would give him the opportunity to climb to the summit once more.

He is aware, too, that the chatter on tour now claims that Murray v Djokovic will be the major rivalry in the sport.

"I think there's a legitimate point about it because they've played some great matches this year," said Federer.

"I guess it motivates me. Annoys me? No. They deserve the limelight as well. It's great that we have a lot of champions out there right now playing the game.

"I was very happy for Andy that he made his move at the Olympics and particularly also at the US Open. So it was always going to be natural that he was going to get more limelight.

"Djokovic, after his incredible year last year, was always going to have limelight on him, as well. Then, plus, they have played good matches against each other."

He expressed hope that Rafael Nadal could return soon to the fray after his injury but insisted the prospects for tennis were "exciting".

He added: "I always knew that Andy and Novak were going to stay around for a long time at the very top. Right now, it seems that they're in their prime and this is when they are supposed to play their best tennis."

Federer, of course, played the best tennis at the O2 last year and it gave him confidence after a season without a grand slam. He went on to win Wimbledon in the summer and is no mood to retire.

The promotional merchandise for the tournament states that "it all ends here".

Federer, the champion, is determined to go on.