Yet its list of catches is very modest for a global sport that one study says is the third most vulnerable to betting fraud through match-fixing, because of the proliferation of low-level tournaments and the difficulty of proving that any player has lost deliberately.

The London-based Tennis Integrity Unit (TIU) was set up in 2008 by all the sport's four governing bodies - the men's ATP, women's WTA, the International Tennis Federation (ITF) and the Grand Slam Board - to address concerns that the betting frauds besetting cricket and soccer were also targeting tennis.

The ATP had convened an independent review after a match between Russian former world number three Nikolay Davydenko and Argentina's Martin Vassallo Arguello in 2007 in Poland raised suspicions. Although neither player was found to have committed an offense, the online bookmaker Betfair was forced to void all bets.

Since then, the work of the TIU's five full-time investigators and one data analyst has led to 17 professionals and one official, almost all from the lower rungs of the tennis ladder, being banned for corruption, some of them for life.

But Sunday's revelations from secret files obtained by the BBC and online BuzzFeed News suggest match-fixing exists higher up the food chain, including at Wimbledon, and could involve players currently competing at the Australian Open in Melbourne.

The report did not present any evidence of match-rigging. However, it said 16 players who had been ranked in the top 50 had been repeatedly flagged to the TIU over suspicions that they had thrown matches in the past decade, but that none had been suspended, let alone banned.

A source within the TIU said the article was based on "innuendo", and ATP chief Chris Kermode, who sits on the TIU's board, told a news conference in Melbourne: "No player or official is immune from investigation, regardless of their status or position in the sport. Investigations follow where evidence leads."

Vast challenge

The TIU source said the governing bodies had never turned down a request for extra funding to fight corruption, and Kermode rejected the idea that the TIU lacked teeth.

He said it had the right to "interview any relevant person of interest and obtain their telephone, computer and bank records".

However, TIU head Nigel Willerton, a former senior detective in London's Metropolitan Police, said players could refuse to reveal phone records, albeit at a cost. "That's called non-cooperation, and they can be reported and sanctioned for non-cooperation."

Willerton declined to say whether any players on the pro tour were under investigation -- yet the TIU's task is vast.

The team work with players and tournament directors in prevention, education and investigation, but can only scratch the surface of the 21,000 or so professional players covered by the TIU's mandatory code.

Bookmakers offer odds not only on matches in the high-profile grand slams and ATP and WTA tournaments, but also in a host of lower-level tournaments in far-flung locations.

This is what makes tennis the third most vulnerable international sport to betting-related fraud through match manipulation, according to a 2014 study by the International Centre for Sport Security and Sorbonne University in 2014.

The challenge for the TIU will be to demonstrate that it has not turned a blind eye to the sport's most bankable stars while banning far lesser lights such as Greece's Alexandros Jakupovic, Poland's Piotr Gadomski and Arkadiusz Kocyla, and Slovakia's Ivo Klec in the past year.