MELBOURNE, Australia — Nathan Deakes of Australia, the 50-kilometer walk world champion, has withdrawn from the Beijing Olympics because of a hamstring injury.

It is the Australian track and field team's second Olympic gold medal chance lost in the past two weeks following the withdrawal of two-time 400-meter hurdles world champion Jana Rawlinson because of complications from a toe injury.

The 30-year-old Deakes aggravated his troublesome hamstring last week at his training camp at the Swiss resort of St. Moritz, a team official said Monday. An MRI revealed a tear that would require surgery, forcing him out of the Games.

"I'm still in a bit of shock," said Deakes, who is expected to be out of competition for between six and nine months. "I'm sure it will sink in in the middle of August when I'm watching the Games."