Just read an article that said that Ponder hasn't practiced this week due to the injury he suffered on Sunday. Apparently Webb has taken all of the 1st team snaps this week. Peterson practiced on Thursday but isn't certain to start on Sunday either.
There is a Ground Hog day aspect to this story. It's late in the season, and the starting QB goes down. The backup is unavailable (due to injury or being waived), and the team turns to the guy who's been running the scout team all year. Oh, and AP is banged up.
As an aside, it burned my britches that McNabb was getting the back up reps on this team after Ponder replaced him. That seemed pretty short sighted to me given that McNabb wasn't playing all that well to begin with and wasn't going to be on the team past the end of the year.
Regardless of what happens, at least the Lions will have to be thinking about preparing for two possible QBs this week.