It worried me on Sunday as I watched SS Morgan Burnett limping on the sidelines. He appeared to be testing his knee out. Unfortunately it reminded me of week 1 when RB Ryan Grant was limping along the sidelines, trying to prove his ankle was better so he could get back into the game. Just as Grant's ankle injury was season-ending, so is Burnett's knee injury. From Journal-Sentinel:
S Morgan Burnett is out for the season with an ACL tear. McCarthy thinks he played for a few series with the tear.
There's no upside here. S Derrick Martin, who had an INT against the Bears in relief of S Nick Collins, will take over, and I'm still suspicious of him after he messed up the game last season in Minnesota. With backup S Charlie Peprah also injured, I'm assuming that the new backup safety is Jarrett Bush.
Martin is likely to be a temporary starter until SS Atari Bigby returns from the PUP list in a couple weeks. Since Bigby's missed all of training camp and the regular season, there's no word on how he looks until he's eligible to return to the practice field. But they'll be very thin at safety until then.