Jay Glazer notes that Marc Bulger 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's career in 2005, while late Oilers defensive lineman Jeff Alm had the same injury shortly before committing suicide during the 1993 season.
Basketball players Gabe Pruitt (college) and Yao Ming (pro) also both suffered the injury.