David Nelson doesn't know for certain why the Buffalo Bills decided to let him hit free agency.

The Bills might've wished the fourth-year receiver luck because he won't fit in new head coach Doug Marrone's system or because the $1.323 million qualifying offer was more than they wanted to commit.

Nelson, though, is convinced it's because of the season-ending torn knee ligament he suffered on opening day.

"It's tough for me because I feel in my heart -- and this is just me -- the only reason it's happening is because of the injury," Nelson told me in his first interview since the Bills informed him of their decision.

"I feel if I was able to play last year, things would be different 100 percent. For me that's the reason why; they're not sure if I'll be the same player I've been."

The injury not only cost Nelson a season of production and -- a legitimate possibility -- the Bills a victory or two.

Nelson called it "sobering to re-evaluate" his situation. He's coping with the idea that a twisted knee, while engaged in a meaningless block late in a blowout loss to the New York Jets six months ago, has impacted two seasons.

"It's upsetting," Nelson said Wednesday night from his home in Dallas. "It's already hard enough to sit out a year and not be able to be with your teammates on the field.

"Then to find out they're not going to bring you back because -- and this is my opinion -- because of the uncertainty of the knee and doubts if I can be a good player is the hardest part for me."