Roger Federer and Rafael Nadal were among the players to undergo the most drug tests in 2017 but the International Tennis Federation (ITF) have again refused to detail exactly how many times the world's top performers were tested.

The ITF have this week released the breakdown of how often all players on tour were asked to provide a sample in and out of competition, but did not advise on a specific number if the number of tests exceeded seven in each category.

Statistics unveiled by tennis' world governing body reveal that the number of tests conducted is up, 28.45% to 6,293, from 2016 with in and out-of-competition urine and blood screens having increased as a result.

However, the player-by-player breakdown provides an opaque view of how often the planet's biggest names were scrutinised by drug testers in an era where questions over performances across sport are asked like never before.

Both Federer and Nadal are among a throng of players who underwent 14 or more tests, though a handful of those who ended 2017 in the top 10 of the ATP and WTA rankings were not as regularly monitored.

With regard to in-competition testing, women's number one Simona Halep and the Wimbledon semi-finalist Jo Konta were tested no more than six times during the year. In the men's rankings, Stan Wawrinka – who missed the second half of the season after undergoing knee surgery - was the highest-ranked player not to be tested on seven or more occasions.

Notable players who avoided being tested the minimum number of times were Novak Djokovic, another who missed much of the season through injury, and Serena Williams, who didn't play after winning the Australian Open as she gave birth to her first child.

Alarmingly, Russian player Maria Sharapova was tested no more than three times during 2017 in her first season back after serving a 15-month ban for taking meldonium, though she was tested more than seven times out of competition. She returned to playing in April.

Perhaps the most prominent finding from the ITF's player testing summary is the vast number of players who remain untested out of competition.

The governing body have introduced a registered testing pool for 2018 which targets the top 60 players on the men's and women's tours and requires them to declare whereabouts information, having not previously been required to.

Many players therefore slip under the radar and though the ITF insist those individuals are not exempt from out-of-competition testing, crucially they are not required to provide details regarding their whereabouts during the season - making them hard to convene with.

Of those players untested out-of-competition last year, the list includes Japan's Taro Daniel, Australian Casey Dellacqua, Kaia Kanepi of Estonia, Leonardo Mayer of Argentina and Great Britain's Heather Watson.

Rafael Nadal and Roger Federer
Nadal and Federer were tested more than 14 times each during 2017, though each played over half a century of matches Getty Images