Johnson declined to discuss his injury Thursday. Palmer has not practiced most Thursdays this season but has played Sundays. Houston missed his second straight day of practice.
Among the limited guys are four starters: defensive end Ziggy Ansah (abdomen), safety Louis Delmas (knee), safety Glover Quin (ankle) and left guard Rob Sims (shoulder). Also limited -- and appearing on the list for the first time this week -- is defensive end Israel Idonije with a hamstring injury.
Fox said he feels good practicing when he chatted with the media Thursday.
"I was practicing to prepare as if I was going to play," Fox said Thursday about last week vs. Chicago. "But they decided to hold me out. That's their decision. I'm trying to get back as soon as possible whenever we feel like that's the right move."