Knees made headlines on opening Sunday, never a good thing in the NFL.

Two impact players, Houston middle linebacker Brian Cushing and San Diego wide receiver Keenan Allen, were ruled out for their games Sunday and possibly the remainder of the season.

Allen left the field on a cart after suffering what looked like a serious right knee injury with less than 2 minutes left in the first half. He could be lost for the season, a tough turn of events after Allen returned to play from a kidney injury that kept him off the field last season.

Cushing’s diagnosis was only slightly more optimistic. He also hurt one of his knees but walked off the field. Cushing also missed significant playing time with a range of injuries in 2012 and 2013, but started every game last season.