Douglas Robson

USA TODAY Sports

Anyone seeking to influence the outcome of last month's elite ATP World Tour Finals would have faced a hefty ante.

Champion Novak Djokovic pocketed more than $2 million for his week's work, including a walkover in the final against Roger Federer. Merely setting foot on the court in London guaranteed all eight qualifiers a $155,000 participation fee.

But as the gap between tennis' haves and have-nots continues to spread, top players are concerned about the sport's susceptibility to match fixing and other corrupting tactics, especially at the lower-levels of the game.

"I think it's illegal and I think it is ruining the reputation of our sport," Djokovic told USA Today Sports last month. "We don't have any room for that. But the reality is different."

Djokovic knows that reality first hand. In 2006, he was approached via an intermediary and offered $100,000 to fix a match.

How widespread or serious the problem is remains unclear. Since its formation in September 2008 to police against corruption, the Tennis Integrity Unit (TIU) has issued 11 official sanctions, five for life, including one last month for 22-year-old French umpire Morgan Lamri.

The secretive, London-based TIU does not reveal its budget nor will it comment on the record about any of its investigations, according to spokesman Mark Harrison. It is funded by the International Tennis Federation, ATP, WTA and the Grand Slams.

The TIU's cases have involved obscure figures ranked well below the top-100, such as 27-year-old Russian player Andrey Kumantsov, who was banned for life this year for betting and match-fixing. Kumantsov reached a career-high of No. 261 in 2010. He had career earnings of $103,856.

Outside of official sanctions, evidence is growing that criminals are looking for cracks.

"Courtsiding," where individuals try to beat the small delay between actual and live scores by sitting courtside and transmitting data from a match, resulted in an arrest at last year's Australian Open.

This fall the names of Italian tennis players Daniele Bracciali and Potito Starace — both of whom were among a group of five Italians given betting suspensions in 2007-08 — surfaced in a soccer match-fixing investigation.

And in a story published last month by The Guardian newspaper in Britain, a former Interpol officer and director of integrity at the International Centre for Sports Security cited tennis as the third-most vulnerable sport after soccer and cricket.

ATP chief Chris Kermode is aware of the danger. He said authorities take it seriously and did not believe it was "endemic" in the game.

"Sport fundamentally is about being real," Kermode said last month. "As soon as it isn't, then it's a problem."

Access to players

The growth of live match streaming over the Internet, coupled with the far-flung nature of tennis tournaments around the globe, have made it ripe for exploitation for those looking for any nugget of advantageous information.

Still, players continue to worry about 20th century problems. Access to locker rooms and lounges, even though the tours have tried to crack down in recent years, remains troublesome.

"Unfortunately there are a lot of possibilities," Djokovic said. "You can get access to many rooms or buildings or corners where players are usually hiding and talking about some very intimate stuff, about their injuries and so forth."

Mike Bryan, part of the No. 1 doubles team, estimates that 25%-30% of players have been approached to fix matches in person, by email or via anonymous phone calls.

He says he has never had anyone solicit him to throw or alter an outcome, but knows players who have. His biggest concern isn't the top players but those toiling on the edge of solvency.

"When you're playing a Challenger-level or a small tournament and are offered $50,000 and you're a journeyman, what do you do?" he said.

The ATP and WTA tours tout their tough sanctions, education efforts and no-tolerance policy when it comes to corruption. But is that enough?

Privately, officials admit that they lack the resources to monitor thousands of matches.

"That's the problem with gambling and sports," ATP Player Council President Eric Butorac said. "The money that we're playing for isn't high enough."

Addressing pay

Tacitly, authorities might be addressing the economic vulnerability. In a report released Wednesday, the ITF proposed increasing prize money at its Pro Circuit — the lowest level of sanctioned professional tennis and a stepping stone to the ATP and WTA tours — by up to 50%. Purses at the Pro Circuit events run from $10,000 to $100,000.

In its study, the ITF found that the top 1% of male and female players earned more than 50% of all prize money, which in 2013 totaled $162 million for men and $120 million for women. The proposal needs approval by the federation board, which meets in March, and would take effect in 2016.

Nowhere in the report is there a mention of what effect this might have in deterring match-fixing or other illicit activities. However, ITF spokesman Nick Imison wrote in an email that "improving standards of living for players is one factor in many when it comes to the issue of integrity."

"This could be a good first step by the ITF to address the issue," said Ryan Rodenberg, an assistant professor of sports law analytics at Florida State University who has examined how pay disparity in tennis could encourage players to seek alternative money-making schemes.

Players in recent years also have extracted substantial prize money increases from the four Grand Slam events, which are owned independently. Much of it has been aimed at padding early rounds.

But last week the ATP announced a 14% annual increase in prize money at its nine Masters 1,000 tournaments through 2018. The Masters are the highest-level events below the majors.

Kermode recognizes the disparity problem.

"Clearly we've got to be able to provide that tour where someone isn't losing money and it's sustainable, but I want to incentivize them to go up," said Kermode, who has formed a committee to review Challenger-level purses, which are one step below the ATP.

Meantime, risks persist. Butorac, a doubles specialist ranked No. 20, recalled the night he received an unsolicited phone call at his hotel. He promptly reported it to authorities.

He declined to say where it was and whether the person offered money or made threats.

"They told me to not talk about it," he said of TIU officials. "It's definitely a scary situation when you get a phone call."