Ian Thorpe’s bid to swim at his third Olympics faces its moment of truth at the Australian selection trials starting in Adelaide today.

The attempt by Australia’s most successful Olympian to compete in July’s London Games has dominated the lead-up to the national trials, where world champion James Magnussen is looking to attack the 100m freestyle world record.

Thorpe, 29, 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.

But coaches and rival swimmers have warned against writing off the ‘Thorpedo,’ who ruled the pool from 1998 to 2004, taking nine Olympic medals and 11 world titles, while setting 13 long course world records.

Thorpe admits he does not have high expectations in the 100m and 200m freestyle events at the trials after modest results in lead-up events so far. “The most realistic outcome of this is that I will most likely fail,” he said.

Australia’s selection policy is to pick the top two from each event at the trials for the Olympic team, leaving Thorpe no further opportunities afterwards.

But Grant Hackett, one of his main rivals in a golden era of Australian swimming, was not prepared to discount Thorpe’s chances.

“Ian has done so much for the sport of swimming in this country,” Hackett said. “He deserves our support and best wishes. He knows he is up against it, but he knows how to swim well when it counts.”

Australia’s former Olympic coach Don Talbot believes Thorpe’s biggest hope is selection in the relays, for which he would need a top-six finish in the 100m or 200m events.

Thorpe’s 200m freestyle world record (1:44.06) set in 2001 remains the Australian record, but his 100m career best of 48.56secs only places him ninth on Australia’s all-time list at that distance.

Magnussen, 20, who rocketed to prominence winning the 100m world title in Shanghai last year, wants to send a strong message to his London rivals with a sizzling time in Adelaide next ­Monday.

Magnussen, dubbed ‘The Missile’, became a top favourite for the Olympic gold medal after he won the world 100m sprint crown in 47.63 seconds and now has his sights on Brazilian Cesar Cielo’s 46.91sec world record.

“All I want to do is get down in those low 47sec and just sort of throw a cat amongst the pigeons worldwide,” Magnussen said.

At the trials former breaststroke queen Leisel Jones, 26, will be bidding to become the first Australian swimmer to compete at four Olympics.

Triple Olympic gold medallist Libby Trickett is another on the comeback trail and is looking to make her third Olympics after retiring from the sport in 2009.

Trickett, 27, who won the 100m butterfly Olympic gold in Beijing, will be vying for selection in the 50m and 100m freestyle and the 100m butterfly.

Stephanie Rice, a reigning triple Olympic champion, is fighting back from shoulder surgery to make the London team and will be in action in the 400m individual medley tonight.

Rice, 23, underwent an arthroscopy on her shoulder in December after having had more extensive surgery before last year’s world championships. She will face tough opposition from Alicia Coutts, who took silver at the Shanghai worlds in the 200m medley.

Butterfly specialist Geoff Huegill, 33, and sprinter Michael Klim, 34, are also having cracks at reaching another Olympics.