Former Olympic and world 100 metres champion Maurice Greene announced his retirement from athletics on Monday.

The 33-year-old American, who also held the 100 metres world record of 9.79 seconds for more than three years, said a calf injury he sustained in training last month had convinced him to end his career.

"Today I'm officially announcing my retirement from the sport," he told reporters in Beijing [Images].

"I don't think I can have that mental battle with myself coming back from injury any more. It takes a lot out of you mentally ... you start getting down and then you get depressed."

"This is Olympic year, something I wanted to do so bad. So I just decided to call it quits ... I want other people in the sport to shine."

A native of Kansas City, Greene made his breakthrough by claiming the 100 metres gold at the 1997 world championships.

In June 1999 in Athens, he ran a world record time of 9.79 seconds, carving five hundredths of a second off Donovan Bailey's three year old mark.

That same August in Seville, he became first man to win the 100m and 200m titles at a single world championships and a year later he won the Olympic 100 metres at the Sydney Games. He added another Olympic gold in the sprint relay.

His world mark survived until Tim Montgomery ran 9.78 in 2002, although Montgomery was later stripped of the record after being found guilty of using banned substances.

"I've had so many highlights, my first Olympic gold medal, my first World Championship gold, breaking the world record indoors and outside," Greene said.

"All of them mean something to me, something special in my heart. I just wanted to be the best I could be, I wanted to be the greatest of all time."

"A SHOCKER"

Tyson Gay [Images], who matched Greene's sprint double at last year's world championships in Osaka and hopes to repeat the feat at August's Beijing Olympics [Images], was surprised by his compatriot's retirement.

"It's a shocker to me," he told Reuters at a training event organised by his personal sponsors Adidas.

"Not having Maurice Greene around in track and field any more is just like Michael Jordan retiring from basketball, or Tiger Woods [Images] retiring.

"He's the greatest."

Greene, who ran the 100 metres in less than 10 seconds a record 52 times, said he hoped the success of his career would be measured not just by the four Olympic medals and five World Championship gold medals he won.

"I hope people remember me as a great athlete but more than anything as a great person to be around," he said.