Interim coach Leslie Frazier confirmed the information Tuesday during an interview with ESPN 1500 Twin Cities. (Audio available through the same link.)
"We don't think it's any more than an ankle sprain," Frazier said. "Now it's just a matter of what he can or can't do. ... We'll know a little more [Wednesday] as he tries to put some weight on it and move around. We're anxious to find out how he comes along."
Peterson has played in 51 consecutive games and has a substantial pain threshold, but it's tough for any running back to excel with a sprained ankle. At the very least, you can expect rookie Toby Gerhart to take some or all of the first-team repetitions in practice this week and for third-string tailback Albert Young to be active for Sunday's game against the Buffalo Bills.