Lee went down with a left knee injury during the team portion of what was supposed to be a noncontact workout Tuesday. Coach Jason Garrett said Lee was getting an MRI later in the day.
The fifth-year middle linebacker went to the ground with rookie offensive lineman Zack Martin on top of him and didn't get up right away. He had to be helped off the field by trainers, screaming in anger at cameramen lining the entrance to the training room.
The 27-year-old Lee has missed 15 of 32 games the past two seasons and has never played a full a season in his four years in the league. He missed five games last year with hamstring and neck injuries.
"Unfortunately, he's had to deal with a few of these things but he's as mentally tough an individual as I've ever been around," Garrett said. "So whatever the circumstances are he always puts his best foot forward and strives to be his best. Don't anticipate this being any different."
Lee, who wasn't in the locker room when it was open to reporters Tuesday, tore a ligament in his right knee during spring practice at Penn State in 2008 and sat out that season before finishing his college career a year later. The Cowboys drafted him in the second round in 2010.
After a pair of mostly healthy seasons his first two years, Lee sustained a season-ending toe injury in the sixth game in 2012. He finished the season on the inactive list again last year with a neck injury.
Despite playing just 46 games over four seasons, he leads all linebackers with 11 interceptions. He was the team's leading tackler when he started 15 games in 2011.
"Sean's been as committed and hard-working a teammate as I've ever been around," quarterback Tony Romo said. "I love the guy like a brother. He's the epitome of what you want in a football player."
The holdovers on the Dallas roster who filled in at times for Lee last year are Justin Durant and second-year player DeVonte Holloman. Rookie Anthony Hitchens, a fourth-round pick, could play there as well.
More Sports Headlines
Seahawks shut out Bears 26-0 for first win of season Graham shows Seahawks fans what he can do All eyes are focused on Seahawks rookie Lockett Chancellor's return helps Seahawks' defense shut out Bears Seahawks rookie running back Rawls fills in for injured Lynch Prince George routs Silvertips 5-1 M's guaranteed to have losing record after 3-2 loss to Angels Steelers beat Rams; Roethlisberger out 4-to-6 weeks with knee injury
Our new comment system is not supported in IE 7. Please upgrade your browser here.