"We feel badly for Kiko because he has worked very hard this offseason in preparation for the upcoming season, but we look forward to his return with his style of play that made him one of the league's outstanding rookies in 2013," Bills general manager Doug Whley said in a statement.
Alonso underwent surgery to his hip this offseason, and his return to the field was already unclear.
Buffalo has decent linebacker depth with third-round pick Preston Brown a candidate for passing downs, but losing Alonso is a huge blow to their loaded defensive front seven. The Bills also lost defensive coordinator Mike Pettine in the offseason, and have changed their scheme with new coordinator Jim Schwartz in town.
This is a team that needs its defense to lead the way. Playing without Alonso will make that a lot tougher.