(CNN) -- Brad Drewett is reluctant to divulge exact numbers, but the ATP World Tour Finals is a big deal for men's tennis.
The season-ending event, worth $5 million in prize money this year, is the tour's marquee event -- an elite eight-man showpiece that attracts top sponsors and acts as a massive advert for the game.
"It's one the of the ATP's biggest assets," longtime tournament director Brad Drewett told CNN during this week's round-robin matches. "For it to be a commercial success is extremely important for us."
Drewett, a 58-year-old former tennis prodigy, has been running the finals for more than a decade now.
It came to London's glitzy O2 Arena -- best known as a concert venue -- in 2009 after Drewett took it back to Shanghai for three years.
"The actual financial structure is a bit different. We have a partnership here with AEG, the owners of the O2, whereas in Shanghai we had a partnership with the municipal government who were very keen to have the event for the purpose of promoting China and Shanghai and also promoting the sport of tennis in China," he said.
"Here it was us wanting to bring the event back to the traditional market of Europe, and in particular London."
The UK capital has a contract until 2013, but doubts have been raised about the event's future on the banks of the River Thames due to complaints about British laws which require players to be taxed on all endorsements during the time they are in the country.
The Lawn Tennis Association, which runs Wimbledon and is also an event partner of the ATP finals, is lobbying the government for an exemption.
"If we lose events like this it will have a big impact not just on the economy but also on sponsors and television and in other areas," LTA chief executive Roger Draper told the UK Press Association.
Drewett said the ATP is happy for the event to stay in London, which is one of the ruling body's global headquarters alongside Florida, Sydney and Monte Carlo.
"That decision won't be made until the second or third quarter of next year. That's a decision for our board. We're very happy here," he said.
"We have every reason to believe that next year and the following year will be just as popular."
More than 250,000 people attended the 17,500-capacity arena over eight days in the first two years, and sponsorship has "sold out" with title partner Barclays bank joined by luxury-goods brands such as Rolex, Lacoste and Moet & Chandon along with the likes of FedEx, South African Airways, Nissan, Ricoh and Italian power giant Enel.
It is broadcast in the UK by public and subscription channels, and in more than 150 countries around the world.
"It's our marquee event and it generates a significant amount of money for us," Drewett said. "And from a promotional point of view this week is the event that everyone is talking about."
The 2009 rebranding from the Masters Cup has also given the tournament a distinct identity from the four grand slam events of the tennis calendar.
"A grand slam has two or three major courts, men and women, plus the outside courts over 14 days. To have quarter of a million in that time frame on one court is testament to the strength of the event and the players we have right now and their popularity," Drewett said.
"I personally like the rebranding. It tells a good story, it's pretty clear what it is. The message is very clear to the consumer.
"We're not looking to compete in any way with the grand slams. This event is what it is -- the format being eight players, only men, indoors, round-robin -- it speaks for itself as being totally different from a grand slam. The public understand that."
Drewett was one of the most promising young players of the 1970s, winning the Australian Open junior title twice, but was not quite so successful on the senior circuit as he reached a career-high ranking of 34.
However, he did appear at the season-ending event once, in the doubles at London's Royal Albert Hall in 1988 when it was a separate tournament -- now both formats are run during the same week.
At that time, Madison Square Gardens was nearing the end of a 13-year run of hosting the singles -- and Drewett believes that the O2 is taking on a similar status to the iconic New York venue.
"In its time it was one of the special ones, like here. The finals was a very special event. People still talk about playing at Madison Square Gardens, and this is going to be the same," he said.
"When you go out there, the court, the crowd -- there's a certain atmosphere you don't get very often at sporting events."
After ending his career, Drewett became involved in businesses before being asked to run for a place on the ATP board to represent the players.
He did so for five years before taking on the role of chief executive of the ATP's International Group.
"I was always interested in the politics and business. I was interested in what made the tour tick even as a player," Drewett said.
"Tennis has been, in relative terms, pretty big business for a long time. In terms of professional sport it's one of the most mature.
"Tennis was one of the first where pro athletes could make a serious living from it, back in the 1950s. The business has got bigger and more mature, and it's as strong as it's ever been 60 years later."