Chiefs quarterback Matt Cassel has a rib injury that could keep him out of the team's season opener against the Bills on Sept. 11.
Tyler Palko is the No. 2 quarterback behind Cassel, but he has never started an NFL game.
Cassel appeared to suffer the injury on a hit from 340-pound defensive tackle Howard Green in Kansas City's preseason finale against Green Bay.
Cassel Could Be Sidelined For Opener