49ers' Clark out for at least two to four more weeks.

Byline: Dennis Georgatos

STOCKTON, Calif. _ Tight end Greg Clark underwent hamstring surgery Tuesday for the third time in six months and will remain sidelined for at least two to four more weeks. The latest operation raised doubts about his availability for the 49ers' opener Sept. 9 against Atlanta.

"That's up in the air," Coach Steve Mariucci said. "He could start practicing in two or three weeks but then you have to decide if he's really ready to play."

In a worst-case scenario, Mariucci conceded Clark, one of the top blocking tight ends in the league and an important part of the rushing attack, could be out for as long as six weeks.

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