Already under enormous pressure to break into Australia's Olympic swimming team as the headline act of this week's national trials, Ian Thorpe was forced to wade into controversy on Wednesday over preferential payments made to marquee swimmers.

Australia's Ian Thorpe speaks to journalists after competing in his men's 100m butterfly heat at the FINA Swimming World Cup in Tokyo, Nov 13, 2011. [Photo/Agencies]

Local media have reported disaffection within Australia's swimming ranks over alleged preferential funding benefiting former Olympic champions on the comeback trail like Thorpe, Michael Klim and Libby Trickett in the days leading up to the trials that start on Thursday.

Reports have questioned the value of funding Thorpe's comeback ambitions, which has entailed providing individualized training overseas in Switzerland and the Middle East, while other front-line swimmers have trained at home and shared coaches.

Thorpe denied receiving preferential funding, which local media have estimated cost Swimming Australia A$150,000 ($158,000) - up to 10 times the amount given to other swimmers.

"Firstly, I haven't been paid a cent," five-time Olympic champion Thorpe told reporters at the South Australia Aquatic and Leisure Centre, the venue for the trials that start on Thursday. "It's been clarified by a number of people that what's been reported isn't factual.

"There's been a number of athletes who've been Olympic champions or world record holders who have been supported by Swimming Australia.

"The funding that's come from that is not dissimilar as to what's been funded for other people in this sport.

"There hasn't been any preferential treatment, as such, given.

"There may be a higher cost because I'm training outside (Australia) and it's not shared amongst a number of athletes, that's it."

Thorpe, whose image dominates promotional material at the meeting and around South Australia's state capital, has attracted a huge media presence to the trials, despite the swimmer all but writing off his chances to make the team.

He will compete in the 100 and 200 meters freestyle events, with most pundits forecasting his only hopes of selection for London lie in cobbling a spot on the relay teams.

Swimming Australia has conceded Thorpe's program overseas may have cost more than preparing domestically-trained swimmers but has pointed to the raised attention the swimmer's comeback has brought back to the sport.

A flop of their headline act in the trials would nonetheless be an embarrassment for the governing body, whose head coach Leigh Nugent has backed Thorpe to the hilt and shot back at critics that have said the swimmer left his run too late to be fit for London.

Thorpe was offering little comfort on Wednesday, two days before he swims the 200 freestyle heats. "I'm not sure how fast I can go at this stage and like most of the other athletes here, I am nervous about the upcoming days," the 11-times world champion said.

"It's going to have be much faster than what I've swum previously.

"What I said was that I'd come to terms with, this is what could happen, that I more than likely could fail in this.

"But once you can kind of accept that you can let yourself go and be able to do what's necessary to be able to prepare and be able to train without having that level of fear in what you're trying to accomplish.

"I'm probably as confident as I've been in my preparation, I'm happy with how I've trained recently and I'm looking forward to the competition."