Vikings running back Adrian Peterson has a high ankle sprain that will put him in a walking boot this week, leaving his availability for Sunday's game at Atlanta in question. Minnesota coach Leslie Frazier said Monday that Peterson has a Grade 1 sprain, the least severe of the three categories, with "a little bit of" ligament damage. "The good news is there's nothing more serious than that," Frazier said, adding: "He'll recover from it. It's just the amount of time that he'll miss. We'll have a better indication toward the end of the week."