Where top FPR teams could falter

The 49ers were incredibly healthy last season. Will that continue in the future? Kyle Terada/USA TODAY Sports

The NFL Future Power Rankings didn't exist 24 months ago. If they had, a conservative estimate of where the currently No. 1 San Francisco 49ers would have landed would be somewhere from No. 24 to 28.

Consider the situation in June 2011: The team is coming off an oil spill of a 6-10 season and is now in the midst of a coaching transition. They are saddled with the antithesis of a franchise QB -- in a league where elite quarterbacking determines plenty, the 49ers have sixth-year pro Alex Smith, who just finished his best NFL season so far ranked 28th in QBR. The QB waiting in the wings? Troy Smith! The 49ers defense has some good pieces, but ranked 16th in total defense in 2010. The offense lacks weapons outside of Vernon Davis, scares nobody and ranked 24th in scoring.

Recent hindsight has made us take the brilliant coaching of Jim Harbaugh for granted; it tends to make people think things were more optimistic; it convinces us we really could see the silver lining. But we didn't. The future at that point was as inspiring as a Mike Singletary halftime pep talk.

Fast-forward to June 2013 and the 49ers appear built to contend for titles for years to come; they're a strong No. 1 overall in the first 2013 NFL Power Rankings. But let this serve as a reminder: In football, things change. And quickly. So, for the teams at the top of the rankings, I was asked to provide one reason apiece why the ranking you see today could plummet the next time we add it up. Top teams, I hereby warn thee.

Here's where it could easily go wrong.

1. Where the 49ers go wrong: Injuries become a reality
The 49ers front office deserves every ounce of praise it receives for building what is widely considered the NFL's deepest roster. But in the same way GMs might grouse about how smart the Colts front office is sure to look for years because they backed into Andrew Luck, they're doing the same right now about San Francisco's remarkable run of good health.