Despite the injury, Dallas will have to sign Brewster to a deal based on his draft position. After that, he may be placed on the physically unable to perform list, or injured reserve.
Dallas remains hopeful that all will agree to terms in time to attend the first practice, on Wednesday morning.
McGee will likely begin the season behind Tony Romo and Jon Kitna, and doesn't figure to get any significant time under center during the regular season. Drafted in the fourth round, this was something of a controversial pick, as his career in College Station was hampered by injury.
Williams, a third rounder out of Western Illinois, will be used to add depth to the Dallas pass rush in the absence of Greg Ellis.