Dec. 24, 2011: Peterson injures his left knee in a Christmas Eve victory over the Redskins in Washington, D.C. The injury happens when he plants his left leg and is tackled by safety DeJon Gomes early in the third quarter.

Dec. 30, 2011: Peterson undergoes surgery to repair torn anterior cruciate and medial collateral ligaments in his left knee. Dr. James Andrews performs the surgery in Birmingham, Ala.

Jan. 13: Peterson is walking without crutches. He said of watching the replay of his injury: ""My stomach crawls just looking at it. Your leg is not supposed to go that way. At all."

March 26: Peterson is cleared to begin running. Says Vikings coach Leslie Frazier: "He's a guy who wants to defy the odds with this injury. He wants to do things when he comes back that no one with an ACL tear has ever done."

Wednesday: Peterson runs drills for the media and says he believes he will play in the season opener Sept. 9 against Jacksonville.