Jay Glazer notes that Marc Bulger [1] has a fracture in his lower leg (his fibula?) and will be out 3-6 weeks.
UPDATE: Bulger has a "tibial plateau fracture".
The closest comp for that sort of injury is a coach -- it's the injury Joe Paterno suffered when his leg was rolled over a few years back.
Besides that, the only records we have of NFL players suffering the injury are linemen. Such a fracture ended Bengals lineman Rich Braham [2]'s career in 2005, while late Oilers defensive lineman Jeff Alm had the same injury [3] shortly before committing suicide during the 1993 season.
Basketball players Gabe Pruitt (college) and Yao Ming (pro) also both suffered the injury.
Links:
[1] http://www.footballoutsiders.com/player/15523/marc-bulger
[2] http://www.footballoutsiders.com/player/17626/rich-braham
[3] http://www.nytimes.com/1993/12/15/sports/pro-football-a-friend-dies-and-oiler-kills-himself.html