http://espnwisconsin.com/common/more.php?m=49&action=blog&r=40&post_id=13701
While his two compadres from the physically unable to perform list – tight end Andrew Quarless and outside linebacker Frank Zombo – have started their second week of practice en route to returning to the Green Bay Packers’ 53-man roster, second-year tackle Derek Sherrod is still in a holding pattern and apparently won’t begin practicing this week.
“That’s on Doc,” Sherrod said Wednesday, referring to team physician Dr. Pat McKenzie. “If it was on me, I’d be practicing months ago. I just have to take it day by day.”
Sherrod suffered a gruesome broken leg Dec. 18 at Kansas City that required immediate emergency surgery.
“I feel very close,” he said Wednesday. “I’m still not 100 percent, but I’m getting closer each and every single day.”

To what degree I think both theories are true, I don't know - I too have seen a lot of catastrophic leg injuries to players over the years that have ended promising careers. I'm not a surgeon to be sure but when you have a broken major support bone in a leg, and then an ankle problem to boot, on a very large body ... yeah ... I can see serious mobility issues on this young man's horizon.