Australia's Ian Thorpe waits to compete in the men's 100m freestyle heat at the FINA Swimming World Cup in Tokyo November 12, 2011. [Photo\Agencies]

Ian Thorpe's bid to make Australia's swimming team for the London Games after coming out of retirement is more than likely doomed to fail at next week's national trials in Adelaide, the five-times Olympic champion said.

Thorpe, who announced his return to the pool just over a year ago after retiring in 2006, told Australian television he had left his run too late.

"The most realistic outcome of this is that I will most likely fail," Thorpe told Network Ten.

"I wish I had another six months to do this. I wish I had more time to do it."

Thorpe will compete in the 100 and 200 metres freestyle events at the March 15-22 trials but remains well short of the pace needed to book a spot at a third Olympics.

The 29-year-old clocked a pedestrian 52.28 seconds in the 100 freestyle in Zurich last month, a time unlikely to secure him even a relay berth in Adelaide.

He swam the 200 in one minute 50.79 seconds at a state championships meeting in Melbourne in January, more than six seconds shy of his 1.44.06 world record in 2001, which stood for almost six years.

Thorpe also failed to impress at a number of meets across the Asian World Cup series since his comeback to competitive swimming in November.

Despite the swimmer's own concerns about his progress, Australia's head coach Leigh Nugent and former champions, including twice 1,500 freestyle Olympic gold medallist Grant Hackett, have refused to write him off.

Thorpe said failure at Adelaide would not mean another prompt retirement.

"It's probably the last time that I'll be able to do this, so I want to make the most of it," he said.

"So I'll probably swim for at least a year or two after the Games."