Whether he’s ready or not, the Patrick Peterson era is about to start in Arizona.

A torn ACL has ended Greg Toler’s season before it was able to begin, likely forcing the rookie Peterson into a starting role. The No. 5 overall pick was supposed to be eased into the Cardinals’ lineup, but with Dominique Rodgers-Cromartie now a Philadelphia Eagle and Toler on the injured reserve, Peterson will likely start for Ken Whisenhunt from the get-go.

Peterson will be paired with another unproven youngster in A.J. Jefferson, who barely played as an undrafted rookie last year. Peterson and Jefferson have two games of experience between them.

Expect veteran Richard Marshall, who was signed as a free agent this month, to play a pivotal role. Marshall and Michael Adams are the only cornerbacks on the roster with starting experience, but Adams is also hurt right now.

Just 18 months ago in Arizona, Antrel Rolle and Rodgers-Cromartie made up one of the most talented young corner duos in the league. Rolle, a two-time Pro Bowler, was released for financial reasons before signing with the Giants last offseason. Rodgers-Cromartie was dealt to the Eagles for Kevin Kolb earlier this month.

Now, it’s a dire situation for a defense that gave up an ugly 7.3 yards per attempt and 56 completions of 20-plus yards with┬áRodgers-Cromartie in 2010.