"I don't think anyone will win eight but if there is any person on the planet that can, it's Michael Phelps," Thorpe told Reuters on Monday.

The 23-year-old American swimmer is setting himself the ultimate target in his sport -- trying to better Spitz's Munich haul of seven golds.

Thorpe, 25, who retired from swimming two years ago and now just takes to the pool for relaxation, said: "I don't think he can't do it, I just don't think he will. Look at the competition."

Phelps won six gold and two bronze medals in Athens and this time the multiple world record holder is going for the same events -- the 100 and 200 butterfly, the 200 and 400 individual medleys, the 200 freestyle and three relays.

"There is a lot of competition, even in the events he is really strong in. They are going to be tough races for him. I think it is going to be the schedule that makes it difficult. He also has to rely on relays.”

"I think the competition for him is tougher here than what it would have been in Athens certainly," he added.

Phelps has said Thorpe's pessimistic prediction has helped to motivate him.

Thorpe was delighted to hear that: "I am happy. I am friends with Michael.”

"I am going to tell him if I see him before the competition that if there is anyone that is going to do this it would be you -- and I would like to watch it happen."

Asked about the rivalry in the pool between swimming superpowers the United States and Australia, the five-time Olympic gold medallist said: "It's a great one for livening up the press. That's about it.”

"For the most part we are good friends but we like to beat them. Everyone likes to beat the Americans."

Thorpe is currently suing French sports newspaper L'Equipe over reports he used performance-enhancing drugs during his career, his lawyer said on Monday.

One of the greatest swimmers of all time, who is also a prominent anti-drugs campaigner, would not comment on the allegations but has in the past said his reputation was permanently tarnished by the accusations, which he called "gut-wrenching".

After years of punishing training schedules and interminable lengths up and down the pool, Thorpe now just dives in to unwind for 15 to 45 minutes at a time.

He enjoys swimming now: "It has become more personal for me. I swim on average three times a week. So I obviously get stressed three times a week.”