Patrick Willis, perhaps the team's only consistent force on defense, to say nothing of his leadership, would miss the remainder of the season. The culprit being a toe injury that seemed fairly benign, but managed to knock him out of action for several weeks before it was finally determined that surgery would be needed, ending his season before it ever really got going.
This wouldn't have been good news even if things had been going well for the 49ers, but given that Navorro Bowman has yet to play or even practice this season (the window for him to be allowed to practice at all this season shuts on Tuesday) and Aldon Smith is only now returning from his suspension (and who knows how that will go), a thin 49ers Linebacker unit losing its anchor feels that much more devastating.
Without Willis, the 49ers defense has been shorthanded, but they've still managed to play at a high level, which is a credit to both Defensive Coordinator Vic Fangio, as well as Willis' replacement at inside Linebacker, Rookie Chris Borland. Though Borland is no Willis and will never be, Borland has kind of come out of nowhere to play really well, racking up 35 tackles in the past two games and being generally disruptive against the run and the pass. He also scooped up Drew Brees' fumble in Overtime on Sunday, setting the stage for the 49ers to win the game. Credit ought to go to Willis as well; Borland had seen some spot duty filling in the spot that Navorro Bowman would have been in were he available, and Willis has long had the habit of making the players next to him that much better. Hard to say Bowman would have become what he is now without the benefit of playing next to someone of Willis' stature, and lesser players like Michael Wilhoite and now Borland have emerged to have fine seasons—particularly Borland in this instance.
Still, for as well as Borland has played, he's still a Rookie and an unknown commodity at the kind of position where you tend to get overlooked unless you're Patrick Willis, or Lawrence Taylor, or some sort of other monstrous, otherworldly presence at that particular position. Willis is one of those players that everyone rallies around, a leader on the team in every sense of the word even though he might not have the panache of a Colin Kaepernick or Vernon Davis. Nobody's been more important to the team over the past 8 seasons and to now have to do battle without him is a blow that shouldn't be glossed over.