Alonso suffered a torn ACL while working out earlier this month and is expected to miss the 2014 season.
A second-round pick out of Oregon in 2013, Alonso, 23, recorded 87 tackles and two sacks while starting every game for Buffalo last season.
The Bills also signed free agent linebacker Stevenson Sylvester, who appeared in 50 games -- mostly on special teams -- over the past four seasons for the Pittsburgh Steelers.
Buffalo won six games and missed the playoffs last season.
- Chris Johnson