Dallas Cowboys starting defensive end Marcus Spears injured his knee towards the end of today's afternoon practice, Calvin Watkins of ESPNDallas.com reports.

Spears was carted off the field and is expected to undergo an MRI.

Todd Archer of the Dallas Morning News reports that the fear is that Spears sprained the MCL in his knee, which could sideline the former first-round pick for up to six weeks.

The 6-4, 309-pound Spears has started 71 of his 80 regular season games with the Cowboys, totaling 166 tackles and 8 quarterback sacks. Dallas tendered him at the "Original Round" level, which will pay Spears a non-guaranteed base salary of $1.226 million in 2010.

Reserve offensive tackle Alex Barron, who was chosen by the St. Louis Rams in the spot ahead of Spears in the 2005 NFL Draft, dislocated his left pinkie finger today, as well.