WESTERN Bulldogs midfielder Clay Smith appears to have suffered the third serious knee injury of his short career after opting to return to Saturday's clash against St Kilda after an earlier injury scare.   

Beveridge: 'It's tragic'

Smith, who endured two knee reconstructions in a 12-month period before returning for the Bulldogs two weeks ago, suffered the injury as the half-time siren sounded during Saturday's clash against St Kilda.

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The 21-year-old was leading towards the ball when his right knee buckled under him at Etihad Stadium. He was taken from the ground on a stretcher. 

The anterior cruciate ligament in Smith's right knee has been ruptured twice and there were unconfirmed fears on Saturday he had suffered the same injury again.   

Earlier in the second quarter, Smith appeared to jar his right knee near the boundary line – although not on the synthetic turf. 

He was taken to the rooms and assessed by club medical staff before returning to the boundary and testing the knee with a series of run-throughs and returning to the field.

The second incident occurred just 15 minutes after the first.

Coach Luke Beveridge said he hadn't spoken to Smith post-match and he didn't wish to elaborate on the incident.   

"We don't really know the detail and it's difficult for me to talk about it because it's a pretty emotional incident and it effects everyone around the place," he said.

"Without knowing the full extent and the detail, I don't want to comment too much on it."

Smith was recruited with pick No.17 in the 2011 NAB AFL Draft and has played 34 games in four season.