Clinton Portis vs. Bruised Ribs
OK, so this isn't really a key matchup per se. But it is a huge factor for the Lions. If Portis is too injured to play, the Lions would catch an unmeasurable break. Mike Anderson and Quentin Griffin would be the starters for Denver if Portis were to be out. Really, no matter who runs behind this line, they will gain some success. But Portis would be successful behind the majority of offensive lines. Yes, even this one. This injury means a lot to the Lions.
Lions defensive line vs. Broncos offensive line
Bottom line here, the Lions need much better play from their defensive ends. Robert Porcher, James Hall, and Kalimba Edwards have combined for 0 sacks this year. They need Edwards to be fully recovered from his hernia injury, and they need more out of Porcher. The tackles should be fine, but the Broncos offensive line has dominated everyone. Their RB's have been stellar the past several years, dating back to Terrell Davis, all the way up to Mike Anderson, Olandis Gary, and now Clinton Portis. The line will not only need to pressure Jake Plummer into making bad decisions, they will need to stop the outside run. Good luck.
Lions special teams vs. Broncos coverage teams
Special teams is a really underrated aspect of the game. The way the Lions have been moving the ball, they will need optimum field position in order to score points. The always dangerous Az-Zahir Hakim will be returning punts, and he could very well punch one in. But he's going to need to at least put the offense in decent position when he gets the chance.