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...

...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...

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...

...before the Cardinals' NFL football game against the Chicago Bears in Chicago. Morey says he played with a concussion against the Bears despite his role raising awareness about the head injuries. (AP Photo/Nam...