Australia's greatest Olympian Ian Thorpe does not believe Michael Phelps will succeed in his quest to win a record eight gold medals in Beijing.
The 23-year-old American swimmer is bidding to better Mark Spitz's haul of seven gold medals at a single Games.
But the retired Thorpe, a five-time Olympic swimming gold medallist, said: "I don't think he will win eight golds.
"If there is any person on the planet who is capable, it is him. It's sad, but I don't think it will happen."
Phelps fell short of Spitz's 36-year record four years ago when he won six gold and two bronze medals in Athens.
The multiple world record holder will swim the same events this summer as he did in Greece: the 200m and 400m individual medleys, the 100m and 200m butterflies, the 200m freestyle and the three relays.
But Thorpe said Phelps would struggle to better Spitz's achievement, set in Munich, because his old rival was not as dominant in some events as he was in Athens.
"You've got to look at each of his individual races, he's up against incredible competition at the moment," added Thorpe, who retired from the sport in 2006, aged 24.
"Phelps is the greatest swimmer I have ever seen. He's got the whole package"
"It's going to be really though. I wish him all the best to do it because I would love to see it happen in Beijing. I'm sure everyone else would as well."
However, Ian Pope, coach of Australian 1500m swimmer Grant Hackett, believes Phelps has the mental toughness to at least equal Spitz's feat.
"He will match Spitz's record," said Pope. "He's the greatest swimmer I have ever seen. He's got the whole package.
"He's good mentally, he's technically so much better than the rest of the world. He's simply brilliant."
Meanwhile, Pope said Hackett was in prime condition to become the first man in 104 years to win the same swimming event in three consecutive Games.
The 28-year-old has undertaken a gruelling training regime and an unorthodox routine which has earned him the nickname 'Beijing Bubble Boy'.
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"Grant's just been very particular about doing everything correctly. They can call him whatever they like, but at the end of the day he has remained healthy and that's the important thing," added Pope.
"There's no point going to the Olympics to get sick. Grant has had the best preparation and this is the best he has been for many years.
"He's had the fastest times, he's healthy and we've maintained consistent training which is crucial for someone like Grant who is so driven and pushes himself into the ground."
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