You often hear that teams are one piece from contending. That, if they could find a solitary player, they could go from also-rans to Super Bowl contention. What is implied but not said there is that there's a spot on their roster where they have a weak link, a player in desperate need of replacement.

So, as the regular season enters the latter stages, I'm going to take that approach. That means looking at 10 players teams simply have to replace if they want to make the leap from bad to better or from good to great.

Note: All numbers in parentheses are Pro Football Focus grades. For more on our grading system, click here.

Minnesota Vikings: Christian Ponder, QB (-11.4)

Although Ponder is coming off one of his most assured performances of the year, let's not forget this was a make-or-break year for the Vikings' first choice in the 2011 NFL draft. With the team languishing at the bottom of the NFC North, it's safe to say he's been more "break" than "make." Our fifth-lowest-ranked quarterback on the year (ahead of Terrelle Pryor and Chad Henne), Ponder lost his safety net in Percy Harvin, lost his job briefly to Matt Cassel and to Josh Freeman and might lose his roster spot next year if the team decides cutting ties is best with a likely high draft pick coming in.