Andy Murray has called for more out-of-competition doping tests to be carried out in tennis.
The US Open champion, who is taking part in this week's Paris Masters, had previously expressed a dislike of random drugs tests and was particularly outspoken when subjected to one during this year's Australian Open.
However, the Scot admits he has been shocked by the recent revelations about cyclist Lance Armstrong and is keen to avoid a similar controversy in his own sport.
"I think tennis at the top level has been pretty clean" - Andy Murray
"The out-of-competition stuff could probably get better," the 25-year-old told the Daily Mail.
"When we're in December, when people are training and setting their bases, it would be good to do more around that time.
"I've probably had four or five blood tests this year, but a lot more urine, so it's obviously completely necessary when you hear things like about Armstrong."
The Scot continued: "It's a shame for their sport but how they managed to get away with it was incredible, for so long.
"The one thing I would say with a sport like cycling is it's purely physical, there's very little skill involved in the Tour de France.
"It is the power, how many watts you're producing, whereas with tennis you can't learn the skill by taking a drug.
"I think tennis at the top level has been pretty clean compared to most sports. But that isn't to say more can't be done to make 100 per cent sure there are no issues."