Brad Biggs has tweeted:
Strong-side linebacker Pisa Tinoisamoa is also out about a month, maybe a little more, with a right knee sprain. The Bears could need special teams help as well with Trumaine McBride signed. Shaw, who was released by Jacksonville at the end of the summer, is flying in tonight. He will likely sign the contract on Tuesday.
Also, Vaughn McClure is reporting that Pisa could play Sunday:
pisa is day to day with a knee sprain. could play sunday
He adds an explanation as to why Urlacher is done:
12 weeks in a cast followed by 4 weeks of recovery.