Avril was going after Minnesota Vikings quarterback Christian Ponder when his leg buckled after he tried to change direction. No one made contact with Avril, which never is a good sign. He lay crumpled on the ground for a while with what the team called a "back" injury.
Avril gingerly limped off the field under his own power before heading to a trainer's table, and the Lions went on to lose 20-13.
Avril recorded 11 sacks last season. He was given the franchise tag by the Lions and briefly held out before signing the $10.6 million tender before this season.
Lions wide receiver Calvin Johnson also took a big hit to the helmet from Vikings linebacker Chad Greenway, drawing an unnecessary-roughness penalty. The Lions gave Johnson a concussion test on the sideline, but he returned to the the game one series later.Follow Gregg Rosenthal on Twitter @greggrosenthal.