Vic Fangio's San Francisco 49ers front seven was widely viewed as the NFL's best entering last season.
In guessing the length of Smith's absence, this was essentially a worst-case scenario.
With All-Pro inside linebacker NaVorro Bowman stashed on the PUP list for at least six games and run-stuffing nose tackle Glenn Dorsey recovering from a torn biceps, Fangio will have to make do with less talent for half of the season.
While there is plenty of depth on hand thanks to recent draft picks such as Corey Lemonier, Tank Carradine, Chris Borland and Quinton Dial, the drop-off from first-team All-Pro to role player is steep.
It's Smith's absence that could be the most debilitating, however. Entering his fourth season, he has averaged the most sacks per game (0.98) since it became an official statistic in 1982.
If Justin Smith takes a step back in his age-35 season, Fangio will have to make scheme adjustments to cobble together an effective pass rush in September and October.
Although Colin Kaepernick's offense should see significant improvement with a healthy Michael Crabtree and the addition of Stevie Johnson, the defense is in jeopardy of slipping out of the top five for the first time in the Jim Harbaugh era.
Every year, at least one of the consensus NFL superpowers takes a step back and -- much to the dismay of its shocked fan base -- misses the postseason.
Gregg Rosenthal suggested on the recent NFC Preview episode of Around The NFL Podcast that the 49ers are the team most likely to fall on hard times in 2014. If they can't adequately replace two of the most dominant defenders in football, that prediction is going to look prescient in four months.