Five-time Olympic swimming champion Ian Thorpe failed to qualify for the London Games on Sunday but said he had no regrets about returning to the pool and vowed to continue his comeback.

Thorpe lost his last chance to make it to this summer's Games after failing to make the semi-finals of the 100-metres freestyle after missing out on the 200m freestyle earlier in the Australian selection trials.

The 29-year-old won his heat but posted 50.35 seconds which was the 21st fastest time behind world champion James Magnussen (48.26) and his Olympic odyssey was over.

The Olympic great, who had retired in 2006, said the bitter disappointment would not stop him from planning ahead to his next competition.

"I'm still swimming. I wanted to start racing again, I wanted to be competitive again and I wanted to go to the Olympics," he said after failing to make the cut.

"I still want to do all of those things. I've missed out on what was a huge goal for me to accomplish in this short period of time, but still the desire I had before this, it's still there. I still want to swim."

Thorpe said he has no regrets about returning to the sport, adding he hoped to turn the failure into a "great motivator".

"I'm disappointed that I really haven't been able to race in a way that's reflective of the work that I've done and how I've trained. But I don't regret giving this a go," he said.

Thorpe was coy on the chances of a tilt at the 2016 Olympics saying he would "not rule anything out".

But he was more frank when asked whether he felt his legend had been diminished by his failure to qualify for London.

"Possibly. When I started this I realised that was a risk, that I would damage what people's memories were of what I did.

"I was happy to put it at risk because I saw more value in doing this and trying it out, than whatever I would do to those accomplishments that I had before. I think most people can understand that."

Head coach Leigh Nugent said Thorpe was almost there with his swimming but had paid for his inactivity since his 2006 retirement.

"Another couple of months wouldn't have been enough to get Ian to 1:46 or 1:45 (for the 200 freestyle)," Nugent said.

"Not swimming and training for almost six years, training at the intensity he used to train at takes a lot to regain that fitness and background.

"He needs another six or seven months to then go into another highly intense training that he's used to and that his body responds to."

World champion Magnussen, who topped the 100m freestyle heat qualifiers, paid tribute to Thorpe.

"Thorpey has been someone I've always admired as a swimmer, so it is upsetting for him and the rest of us do feel his pain," he said.

"It would have been great to have him there in London, it's disappointing that he's not going to be there and all I can do now is focus on my race."

Thorpe, who won a total of five golds at the Sydney and Athens Olympics, has struggled to reproduce anywhere near the times he swam in his prime with a string of disappointing results since his comeback in Singapore in November.

The "Thorpedo" ruled the pool from 1998 to 2004, taking nine Olympic medals and 11 world titles, while setting 13 long course world records.