Swimming star Grant Hackett is surprised at speculation his great rival and friend Ian Thorpe may retire from the sport.

The world is waiting to see what decision Australia's most successful Olympian makes about his swimming future when Thorpe fronts a media conference in Sydney.

There is growing speculation Thorpe may quit the sport altogether after battling motivational problems, injury and illness over the past 18 months.

At the very least, he looks certain to rule out competing in next month's world championships selection trials in Brisbane and next year's world titles in Melbourne.

The 24-year-old has not competed at a major international meet since the 2004 Athens Olympics.

Hackett, who has swum with and against the all-conquering Thorpe for nearly a decade, said he had not spoken to Thorpe since news of the champion swimmer's latest motivational battle broke last weekend.

But the world and Olympic 1,500m champion said Thorpe had showed no sign of loss of motivation the last time they spoke.

"If there was talk of retiring, and he said it tomorrow, I'd find it hard to comprehend," Hackett said.

"I spoke to him a couple of weeks ago and he sounded very motivated towards Beijing. But he's the only one who can answer those questions.

"I'm fairly intrigued and interested to see what he's going to announce, just like everybody else."

Hackett said he would love Thorpe to continue swimming on to the Beijing Olympics in 2008, but only if he believed it was the right decision for him.

The pair are firm friends as well as long-time rivals, with Hackett offering Thorpe any help he required via text message on Sunday as news broke that Thorpe was unlikely to compete in the nationals and worlds.

"As a friend of Ian's I want to make sure he's happy with the direction he's taking," Hackett said.

"But personally I'd like to see him swim on and swim fast.

"I've always enjoyed competing against him. I want to see him back there swimming fast.

"Hopefully he will make a decision for himself, and does what he wants to do."

But Hackett warned of the dangers Thorpe faced if he considered taking another extended break, saying the longer a swimmer left the sport, the harder it was to come back.

Hackett spent several months out of the pool and missed the Commonwealth Games this year after shoulder surgery.

"Physically, the longer you're away, the harder it is to come back and be competitive," he said.

"Often if you take a break, the sport's shifted forward and things drastically change.

"But with Ian, it could be different because his times are so good and no one's got near his best times."

As the media camped outside Thorpe's Sydney home, two drug testers added another element of theatre to proceedings when they arrived to conduct a random dope test on the five-time Olympic gold medallist.

Drugs in sport watchdog the Australian Sports Anti-Doping Authority said the timing of the test was a coincidence.

Thorpe remained holed up at home, and is scheduled to make an announcement about his swimming future at midday (AEDT) tomorrow in Sydney.

As well as the obvious void in world swimming Thorpe's retirement would create, there are also financial implications for the five-time Olympic gold medallist because of the millions he is paid in sponsorship deals each year.

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