Cowboys defensive end Anthony Spencer to have knee surgery

Anthony Spencer (left) and DeMarcus Ware will shift from outside linebackers to defensive ends in Monte Kiffin's new 4-3 alignment. (Ronald Martinez/Getty Images)

New Cowboys defensive coordinator Monte Kiffin has seen several key players go down with injuries in the first days of training camp. Anthony Spencer, one of Kiffin's best pass rushers, has been added to the list.

Cowboys coach Jason Garrett confirmed Spencer will undergo surgery on his left knee later this week, as first reported by Todd Archer of ESPN Dallas.

While the Cowboys' second-leading pass rusher last season -- 11 sacks and 27 pressures -- will likely miss two to four weeks following the surgery, he also is expected to be ready for the team's Sept. 8 regular-season opener against the Giants.

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A hyperextended left knee led to a bone bruise in May that has lingered and slowed Spencer in the first week of camp. An MRI confirmed the bone bruise Monday.

Spencer's transition from 3-4 outside linebacker to defensive end in the Cowboys' new 4-3 alignment is considered one of the keys to Kiffin's first season in Dallas and whether the team re-signs their twice-tendered veteran defender.

The Cowboys have already lost up-and-coming backup defensive end Tyrone Crawford for the season with a torn left Achilles tendon and are missing veteran defensive tackle Jay Ratliff to a strained hamstring suffered during a conditioning test.

The Dallas defense struggled down the stretch last year after losing six key starters and backups to season-ending injuries including Ratliff and linebackers Sean Lee and Bruce Carter.

From the Associated Press:

"When you let stuff like that creep into you, that's a cancer for the team," said Jason Hatcher, one of the healthy defensive linemen. "Last year we lost a lot of guys, but I think we played our butts off. We're just going to continue to do that."