It's the third time in five games Gates has been forced to sit with the injury.
Legedu Naanee, bothered by a hamstring injury, is the Chargers' third quarterback. Vincent Jackson, coming back from a calf injury that sidelined him in a loss to Oakland, is to start in Naanee's spot. Right guard Louis Vasquez is out with a stinger.
Chiefs fullback Tim Castille is inactive and will be replaced by Mike Cox.
Chiefs quarterback Matt Cassel is out after having an emergency appendectomy Wednesday morning. He'll be replaced by Brodie Croyle.