The subject of doping in tennis has been very much at the forefront of discussion in recent months after it emerged that the ITF had performed just 21 out-of-competition blood tests in 2011.

"I didn't get tested on blood after the Australian Open and I told the responsible people over there that it was a big surprise for me," said 17-time Grand Slam-winner Federer.

Djokovic, the current world number one, made similar claims last month, saying: "In the last six, seven months I haven't been subjected to blood tests."

"They were much more regular in the past, but they stopped taking them."

Dr Stuart Miller, head of the ITF science and technical department, has suggested that the biological passport method is one that the ITF is considering, whilst also stating that the amount of blood tests carried out must improve.

"We're looking very, very closely at it [biological passport method] and I think there's a reasonably good chance that will be operational probably towards the end of 2013," he said.

Roger Federer is the latest in a long line of tennis players calling for stricter anti-doping measures

"We think we need to increase the proportion of blood testing we do under the programme and we think we could also do with tending to increase the proportion of tests we do out of competition,"

The subject of cost, however, is one that has been considered as a factor in the lack of sufficient anti-doping measures in the sport.

"There will be more funding needed to make all the tests possible and the Grand Slam tournaments should help to finance that as it is in their best interest to keep the sport clean and credible," said Federer.

US Open Champion Andy Murray suggested last week that he would be happy to forego earnings in order to increase the level of testing carried out.

"If it means taking some of the money out of the players' earnings then that's what we have to do because not just tennis, all sports need to look very closely at this stuff." said the Scot.

The biological passport method, which disgraced cyclist Lance Armstrong claims deterred him from doping further after it was introduced in cycling, takes various samples of a competitors biological data and looks for abnormalities in normal biological levels in order to spot doping, as opposed to testing for individual substances.

Federer is the latest in a string of players to suggest that the biological passport method is the best way of ensuring that the sport is clean.

"A blood passport will be necessary as some substances can't be discovered right now but might in the future, and that risk of discovery can chase cheaters away," he said.

The 31-year-old Swiss does not believe that there is a major problem with doping in tennis, however.

"The past years we had something like one case a year and often it had to do with unintentional mistakes made by players," he said.

"But even then they should not make those mistakes and know the rules and live by them."

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