The injury occurred while Alonso was training in Oregon, Whaley said in a team-issued statement this evening.
The club does “not have the details” on Alonso’s injury, Whaley said, but he noted that “early indications are that it may be significant.”
The 24-year-old Alonso had a standout rookie season for Buffalo in 2013, recording 159 tackles, intercepting four passes and starting all 16 games. A second-round selection last year, Alonso is a University of Oregon product.
Rookie Preston Brown, a third-round pick from Louisville, could be among the in-house options to fill in for Alonso, who was to play outside linebacker this season.
UPDATE 9:49 p.m. ET: ESPN’s Adam Schefter reports Alonzo has suffered a torn ACL, an injury that’s anticipated to be season-ending.