"He sprained his calf in practice at camp before we came out, so we held him out," head coach John Fox said. "He'll be day to day."
Jeffery, the club's No. 1 wide receiver, did not play in the preseason opener and Fox said there's no timetable yet for his return.
"He'll be back in Bourbonnais because has to be, he has to get treatment," said Fox, "but I don't know yet."
Jeffery has looked outstanding in training camp, so losing him for any extended period of time would be a big loss for the offense. The Bears are also without first-round receiver Kevin White, who hasn't practiced in more than two months due to a shin injury.
Jeremy Stoltz is Publisher of BearReport.com and a member of the Pro Football Writers of America. He is in his fifth season covering the Chicago Bears full time. Follow Bear Report on Twitter.