Ian Thorpe vowed to press on with his comeback despite his dream of swimming in the 200 meters freestyle at the London Olympics turning into a nightmare at Australia's selection trials.

Five-time Olympic gold medalist Thorpe said he was "utterly gutted" after missing out on the 200m final at the trials on Friday and with it forfeiting the chance to swim in the event he once dominated in London.

Thorpe's hopes of competing at July's Olympics now ride on the 100m freestyle, with the heats at the trials starting on Sunday.

Even if he cannot finish in the top two, he still has a chance of racing in the sprint relay in London by finishing in the top six.

Thorpe, who launched his comeback after five years out of the sport, took some time to console himself after his 200m heartbreak before facing the media to express his disappointment with his performance.

He trailed in 12th fastest in the semifinals and his time of one minute 49.91 seconds was almost six seconds slower than his 2001 world record of 1:44.06. Thorpe broke the 200m world record six times in his stellar career.

But Thorpe said he would continue his comeback, starting with his daunting challenge in the 100m where he will be up against world champion James Magnussen, former world record holder Eamon Sullivan and the cream of Australia's top sprinters.

"I intend to. I've enjoyed what I've been doing. I've enjoyed training again, I've enjoyed pushing myself in the pool and I'll keep on swimming until I feel I cannot get any more out of myself," Thorpe said after Friday's setback.

"After tonight it would be a lot easier not to, but I have another race and I think I have another couple of preparations in me as well.

"I won't keep training unless I think I can do that (return to elite level). That's the thing that has motivated me and it is the only thing that will motivate me in the future."

Thorpe must first overcome his bitter disappointment to set himself up for a shot at the top six in the hotly-contested 100m freestyle.

"You never know. Of the two races, this will be the tougher one to qualify for. That's the way that it is," he said.

"It's not going to be easy, this whole thing was never going to be easy."

Asked if his comeback had been worth the considerable effort, Thorpe said: "After feeling like that, the first thing is that it would have been a lot easier to have not even tried.

"I think it's better to attempt something and fail than it is to not even attempt it, so I'm glad that I've been prepared to put myself on the line there."

Australia head coach Leigh Nugent said Thorpe was an "enigma" and he felt for him.

"I feel for Ian. High performance has all sorts of risks to it. You've got to go with it and, as he said, it's like a fairytale or a nightmare and last night Ian expressed it was a bit of a nightmare for him," Nugent said at the pool on Saturday.

"Ian brings everything. He brought so much exposure, criticism, accolades, everything to Australian swimming. The guy is an enigma here and he's like no one else in how people respond. The pool was packed last night and I haven't seen that with anyone else here."