"At first I just thought I am getting old," Brown said. "I'm going to be a little rusty some mornings. The longer it went during the day I knew something was up. We went in and checked it out and that's what it was."
There is no particular play that caused the injury, more so the grind of 10-year career.
"I didn't get hit or twist it or anything where I could say: `Hey, that is the reason it happened.' We don't know."
Brown will have the procedure on Friday, which means the earliest he would be back is the Oct. 24th matchup at Tampa Bay.
What the Bears do know is that Rex Tucker's return now becomes that much more important. After suffering his third serious injury in as many years, Tucker has been cleared by the medical staff and will begin practicing on Monday.
Steve Edwards, who started 16 games at right guard a year ago, will also be given consideration to replace Brown.
"Edwards has filled in well when we've asked him to so we feel OK but again our numbers are getting down so we do need Rex to come back fairly soon," Lovie Smith said.
C Olin Kreutz had arthroscopic surgery to clean out loose particles in his right elbow but is not expected to miss any games. Terrence Metcalf has been getting reps with the first string offensive line at center the past two days.
"We feel like we're still OK with our offensive line but the numbers are getting a little low," Smith said. "It was really good to get Metcalf some reps this week, he really needed that. Olin doesn't come out very often so we feel like that helped an awful lot."