The difference between replacing Brown and Tillman are the options behind them on the depth chart.
Green is the veteran of the group and will replace Brown at free safety. Gray started nine games last year and will slide in at the strong side.
Johnson and Worrell have little experience, but it's easier for a safety to play earlier in their career than a cornerback that has to go one-one-one with the likes of Randy Moss.
Todd McMillon will get the first crack to play opposite McQuarters. He has only one career start on his resume and made the roster because of his special teams skills. Imagine what Moss and Terrell Owens could do to the secondary if McMillon was picked on in the preseason finale against the Cleveland Browns.
Nathan Vasher has the talent to be a starter in the league, but is not ready for primetime. The Bears moved Alfonso Marshall from the practice squad to the 53-man roster when they placed Brown on Injured Reserve.
Although Marshall can provide additional depth at cornerback, his skills are even more unpolished than that of Vasher's.
Without Tillman in the lineup opponents are going to single out whoever replaces him, which could force defensive coordinator Ron Rivera to resort to more zone coverage in order to protect McMillon.
That's the complete opposite of the aggressive nature the Bears showed in Green Bay, but the reality of playing without Tillman leaves little choice.
Without Boone, the Bears have practically no experience on the interior of the d-line.
Ian Scott has been inactive the first two games of the year, but his 7 games played in the league is the most of any defensive tackle on the roster beside Boone. Israel Idonije made his NFL debut against Green Bay and will prove valuable because he can play both end and tackle.