If they don't practice on Friday, with at least limited participation, then I'll be worried.
The report is that the injuries "surfaced" during the game against the Panthers. But Matthews has had chronic hamstring problems, and I wouldn't be surprised if this quad injury is somehow related. Woodson has been playing with toe injuries for many years. Maybe this is a re-occurrence of that prior injury? Right now, it sounds like the Packers are being cautious because they're familiar with the medical history of both players.
If the worst does come to pass, and either of them miss the game, there will be some problems. The return of LB Vic So'oto is not going to replace Matthews, even against the blocking challenged Bears. I can't remember the last game they played without Woodson, and knowing his replacement would be Jarrett Bush fills me with zero confidence.