(CBS) Vikings running back Adrian Peterson has a torn meniscus in his right knee, and his timetable for a return is uncertain, coach Mike Zimmer told KFAN radio on Monday afternoon.

On the positive side, Zimmer didn’t rule out Peterson playing in Week 2.

Peterson suffered the injury in the third quarter of Minnesota’s 17-14 win against Green Bay on Sunday night. He couldn’t put pressure on the leg and was helped off the field and back to the locker room. Later, Peterson was seen on crutches and in a knee brace.

Late in the 2011 season, Peterson tore his left ACL.

The Vikings lead the NFC North at 2-0.