Miami Dolphins' Ronnie Brown is helped off the field with an ankle injury during third quarter NFL football action in Miami, Sunday, 15, 2009.(AP Photo/Jeffrey M Boan

...third quarter of an NFL football game against the St. Louis Rams on Sunday, Nov. 22, 2009, in St. Louis. Warner was taken out of the game after an injury in the second quarter...

Miami Dolphins' Ronnie Brown, center, is helped off the field with an ankle injury during third-quarter NFL football action against the Tampa Bay Buccaneers in Miami, Sunday, Nov. 15, 2009. (AP Photo...

Miami Dolphins' Ronnie Brown, center, is helped off the field with an ankle injury during third-quarter NFL football action against the Tampa Bay Buccaneers in Miami, Sunday, Nov. 15, 2009

WASHINGTON - OCTOBER 28: National Football League Commissioner Roger Goodell (L) testifies with others before the House Judiciary Committee about football brain injuries on Captiol Hill October 28, 2009 in Washington...

...conference at the Switzer Center. Bradford skipped last year's NFL draft to continue his collegiate career but suffered a season ending shoulder injury against Texas

...Philadelphia Eagles during an NFL football game in Charlotte, N.C., Sunday, Sept. 13, 2009. From Delhomme's 11 turnovers in two games to backup Josh Mc Cown's leg injuries, the Panthers are in...

...in drills during an NFL football training session on Sunday, Aug. 16, 2009, in Englewood, Colo. Marshall has been sidelined the past two weeks to take care of a leg injury and be at his...

...Bengals training room, Monday, Sept. 10, 2007, in Cincinnati, urges NFL football players to keep their heads up when they tackle to help prevent injuries. (AP Photo/Al Behrman

...sent a wide-ranging memo about concussions to NFL teams on Tuesday, Nov. 24, 2009, saying the co-chairmen of the league's committee on brain injuries have resigned and that he is examining potential...

...fourth quarter of an NFL football game against the St. Louis Rams Sunday, Nov. 22, 2009, in St. Louis. Warner left the game in the second quarter after an injury, but Arizona went on...

...third quarter of an NFL football game against the St. Louis Rams on Sunday, Nov. 22, 2009, in St. Louis. Warner was taken out of the game after an injury in the second quarter...

...York Giants in the third quarter of an NFL football game, Sunday, Nov. 22, 2009, in East Rutherford, N.J. Turner is out with an injury. The Giants won 34-31. (AP Photo/Kathy...

...is carried on a backboard after suffering an injury on the final play of the Browns' 16-0 loss to the Baltimore Ravens in an NFL football game Monday, Nov. 16, 2009, in Cleveland...

...medical personnel treat wide receiver Josh Cribbs after an injury on the final play of a 16-0 loss to the Baltimore Ravens in an NFL football game on Monday, Nov. 16, 2009, in Cleveland...