Coach Romeo Crennel said Monday that Anderson hasn't passed tests designed to determine whether he's returned to normal brain function.
"He's in the building and walking around," Crennel said. "Those concussions, you've got to go slow with those. They say rest is the best thing."
Receiver Braylon Edwards (foot), running back Jamal Lewis (hamstring), safeties Sean Jones (swelling in knee) and Brodney Pool (concussion) and linebacker Willie McGinest (groin) also stayed behind in Cleveland to recover.
Crennel said they're all progressing, but McGinest was the only one who practiced Monday, and he left the field after individual drills.
If the injured players are unable to practice Tuesday they won't play against the Bears, Crennel said. The club is focusing on getting everyone back for the Sept. 7 regular-season opener against Dallas.
"We've got 10 days after the Chicago game," Crennel said. "If we can get some good work in those 10 days, the guys have enough experience and have worked together enough for the last year, that they'll be able to jell."
Despite Anderson's continued absence, Crennel said he hasn't started preparing Quinn for a possible start against the Cowboys, which would be his first regular-season NFL start.
Quinn was 14-for-24 for 106 yards versus the Lions. He led two field-goal drives in a little more than a half of playing time.
Copyright 2008 by The Associated Press