"My mother, Lavoyda, unexpectedly passed away Monday at her home in Texas," Urlacher said in a statement. "My first priority right now is to be with my family as we mourn her loss and make the arrangements to lay her to rest. This is a very difficult and emotional time for us and I sincerely ask that you respect our privacy. Thank you."
"You can't replace a guy like that," quarterback Jay Cutler said. "You can't find a guy like that in the league. He's the heart and soul of this organization. We all know he's going through a tough time right now, but we're going to respect his privacy and when he gets back we'll be here for him."
Bears coach Lovie Smith told reporters Wednesday that when he lost his mother in February, Urlacher was one of the first guys to call him.
"I'm lucky to be his coach, but our relationship goes a lot further than that," Smith said, adding that "family comes first" on his team.
"We'll be there to support him in any way we can," Smith said. "Hopefully, we'll have Brian ready to go this week. But, if we can't, we feel good (about our backups)."
The Bears had Monday and Tuesday off after last Sunday's 30-12 victory over the Atlanta Falcons. Urlacher had 10 tackles, an interception and a fumble return for a touchdown and was named NFC Defensive Player of the Week.
The Associated Press contributed to this report.