As the Cowboys prepare to take on the Browns’ potent offense in this season’s opening weekend, they might be missing some presence on the pass rush.

Outside linebacker Anthony Spencer is expected to miss two to four weeks after undergoing arthroscopic surgery on his right knee. The injury was originally diagnosed as a bone bruise, but persistent swelling caused the team to decide on having the procedure.

Spencer played defensive end at Purdue but was moved to the pass rush role in the Cowboys’ 3-4 defense after being drafted in the first round in 2007. He had three sacks in his rookie year playing in a situational role, and is expected to have more of a presence on the field in 2008 despite backing up Greg Ellis.

Fellow linebacker Kevin Burnett, another guy who comes in on passing downs, is also in doubt for the season opener.