Rafael Nadal feels that all the results of the various anti-doping measures in tennis should be made public, but added that he has never had any doubt that his opponents were clean.
Nadal's comments come following similar comments made by Andy Murray and Roger Federer, who both urged the tennis authorities to make more money available for anti-doping measures.
"All the world wants a clean sport and tennis has a good anti-doping program. I never had any doubt about the fact that my opponent wasn't clean. The only thing that ITF or ATP should do is to make all drug controls 100 per cent public," said Nadal ahead of the start of the ATP Tour final, which starts in London on Sunday.
"I don't know how many controls I have done, but doing this way everyone could say if the tests are many or less."
Speaking of the ATP's year-end show-piece at London's O2 Arena, Nadal added that it should be played on different surfaces, including his favourite red clay.
"An edition every 15 could be on clay. I have qualified for 11 years and I always play on indoor courts, but the surface could change," he continued
Nadal had a disastrous start to the 2015 season and saw his ranking drop to 10th in the world – his lowest in a decade – but in recent times approached his best once more, having returned to the top five on the latest world rankings.
"Had I qualified and played five months ago, with the anxiety and the lack of competitivity I had at that time, it wouldn't have made any sense to play here," the Spaniard added.