Buffalo Bills linebacker Kiko Alonso underwent successful surgery Thursday to repair a torn ACL.
Alonso, 23, suffered the injury while working out earlier this month and is expected to miss the 2014 season.
A second-round pick out of Oregon in 2013, Alonso 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 — during the past four seasons for the Pittsburgh Steelers.
The team made more additions at linebacker earlier this offseason, adding veterans Brandon Spikes and Keith Rivers and using its third-round draft pick on Louisville product Preston Brown.
Buffalo won six games and missed the playoffs last season.
BURKE: Kiko Alonso injury may derail Bills' plans for breakthrough year
- Chris Johnson