Knighton's asking price didn't match up with the Ravens' budget, even after they created $9.8 million in salary cap space by trading defensive tackle Haloti Ngata to the Detroit Lions and restructuring outside linebacker Terrell Suggs' contract.
Knighton also drew interest from the Oakland Raiders, New England Patriots and Seattle Seahawks. But the Raiders signed defensive tackle Dan Williams and dropped their pursuit of Knighton after they were unable to agree on terms of their deal.
The 6-foot-3, 331-pound Knighton was one of the top-rated run-stopping defensive linemen in the NFL last year and finished with 30 tackles and two sacks.
For the Ravens, signing Knighton would have gone a long way toward adding some veteran leadership to a defensive line that lost Ngata and also released Chris Canty to save $2.66 million against the salary cap.
"Obviously, we drafted him, Del Rio said. "We thought at that time he was a dancing-bear type, a big powerful man who could stay on his feet. This game is about big powerful men so that guys that have the skill level can do their things.
"We got back together, and he played well in Denver. I appreciate that. I respect that. We have to have those kind of people in our trenches on the offensive and defensive line in order to play the kind of football we expect to play."