Earlier today, the Bills confirmed a Kiko Alonso ACL tear will likely keep him out the rest of the season. While the team has options in Keith Rivers and Preston Brown, Alonso is not someone who can be easily replaced.
Alonso finished third in the league in both tackles and interceptions by a linebacker. As a rookie. Talent like that is incredibly rare. To put it into perspective, take a look at his stats compared to the first linebackers off the board in the past four NFL drafts and their rookie years.
Kiko Alonso ACL tear alters the Bills' defense this year.2010 - Rolando McClain (Keep in mind, he's retired twice already) - 85 tackles, 0.5 sacks, 1 interception
2011 - Von Miller (Won Defensive Rookie of the Year) - 64 tackles, 11.5 sacks, 0 interceptions
2012 - Luke Kuechly (Won Defensive Rookie of the Year) - 164 tackles, 1 sack, 2 interceptions
2013 - Jarvis Jones - 40 tackles, 1 sack, 0 interceptions
2013 - Kiko Alonso - 159 tackles, 2.0 sacks, 4 interceptions
As you can tell, Alonso put up a season in which he arguably should have won defensive rookie of the year. His stats blow away those of the first linebacker off the board (Jones). They compare closely to those taken second (Miller) and ninth (Kuechly) overall in their years. A Kiko Alonso ACL tear is the last thing the team wanted to see, especially coming off such an impressive campaign.
Fans can breathe a bit easier because the Bills' front four is one of the league's best (on paper). Mario Williams, Kyle Williams, Marcell Dareus and Jerry Hughes totaled 41 sacks last year. A pass rush like that is what opens up the second level for playmakers like Alonso. Since the defense can rely on these big bodies, they won't be completely lost without their leading tackler.
Keith Rivers is a veteran replacement, and Brandon Spikes was a solid offseason addition. So the Bills' defense won't fall completely to shambles, but it will miss a rising star this year. Keep in mind, however, that players rarely return to form in the year following ACL surgery. Having this injury occur so far before the season may end up being a blessing in disguise.