Ian Thorpe's swimming career is up in the air with the five-time Olympic champion in danger of missing next year's world championships in Melbourne.

The 24-year-old has been tipped to skip the selection trials starting in Brisbane on December 3, which would rule him out of the worlds, after being ravaged by illness and injury this year.

Thorpe is understood to have missed several training sessions since returning to Australia from a three-month sojourn in Los Angeles in October.

A Swimming Australia insider told AAP that Thorpe was not expected to swim in Brisbane.

"I am concerned that it is moving down that track," the source said.

Thorpe's coach Tracey Menzies said her star charge was yet to be ruled out of the trials.

"Not that I know of yet," she told AAP.

She planned on sitting down with stroke guru Milt Nelms, who Thorpe has been working regularly with this year, in the coming week.

"I sit down with (coach) Milt (Nelms) on Wednesday and we go from there," Menzies said.

Thorpe has not competed at a major international meet since the 2004 Athens Olympics, some 27 months ago.

He has struggled to overcome the energy-sapping glandular fever which ruled him out of this year's Commonwealth Games in Melbourne.

Nelms, who Thorpe trained with for most of his time in LA, said only last month the Thorpedo was still finding his way back to "robust health" and doubted he could return to his best in time for the Melbourne world championships.

The 200m and 400m freestyle world record holder has not competed for more than nine months and only raced nine times in three competitive meets since the Athens Games.

If he were to miss the trials, it would cast enormous doubt over whether Australia's most decorated Olympian will compete at the 2008 Beijing Olympics.

He has struggled for motivation in the past after achieving so much during his teenage years - particularly between 1999 and 2002.

The Thorpedo broke 13 long-course world records during this time and became famous around the world in the lead-up to the 2000 Sydney Olympics.

Thorpe has not broken a world record since 2002 but his best times were so far ahead of the rest of the field that he was still able to secure the 200m and 400m gold medals in Athens after capturing three gold medals in Sydney.

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