Can the Patriots protect Brady?

The Patriots' pass blocking has improved from the start of the year -- but it's not perfect. Jeff Hanisch/USA TODAY Sports

Three of the four teams that played in last season's conference championship games again look like some of the top Super Bowl contenders in the league. The odd team out of that group, the San Francisco 49ers, looks likely to be replaced by the Green Bay Packers.

However, the best teams in early December don't always make it to their league title games. For these four contenders, what are the key issues that could derail their championship runs?

Here are the most glaring weaknesses of each of the four teams:

New England Patriots: Pass blocking